diff --git a/changelogs/unreleased/7998-blackpiglet b/changelogs/unreleased/7998-blackpiglet
new file mode 100644
index 0000000000..72c8a4fdd9
--- /dev/null
+++ b/changelogs/unreleased/7998-blackpiglet
@@ -0,0 +1 @@
+Check whether the namespaces specified in namespace filter exist.
\ No newline at end of file
diff --git a/pkg/backup/item_collector.go b/pkg/backup/item_collector.go
index c40f152a96..af7ffe9ae6 100644
--- a/pkg/backup/item_collector.go
+++ b/pkg/backup/item_collector.go
@@ -741,6 +741,23 @@ func (r *itemCollector) collectNamespaces(
 		return nil, errors.WithStack(err)
 	}
 
+	for _, includedNSName := range r.backupRequest.Backup.Spec.IncludedNamespaces {
+		nsExists := false
+		// Skip checking the namespace existing when it's "*".
+		if includedNSName == "*" {
+			continue
+		}
+		for _, unstructuredNS := range unstructuredList.Items {
+			if unstructuredNS.GetName() == includedNSName {
+				nsExists = true
+			}
+		}
+
+		if !nsExists {
+			log.Errorf("fail to get the namespace %s specified in backup.Spec.IncludedNamespaces", includedNSName)
+		}
+	}
+
 	var singleSelector labels.Selector
 	var orSelectors []labels.Selector
 
diff --git a/pkg/backup/item_collector_test.go b/pkg/backup/item_collector_test.go
index 01c8dd2163..562e6a2c33 100644
--- a/pkg/backup/item_collector_test.go
+++ b/pkg/backup/item_collector_test.go
@@ -224,6 +224,17 @@ func TestItemCollectorBackupNamespaces(t *testing.T) {
 			},
 			expectedTrackedNS: []string{"ns1", "ns2"},
 		},
+		{
+			name:   "ns specified by the IncludeNamespaces cannot be found",
+			backup: builder.ForBackup("velero", "backup").IncludedNamespaces("ns1", "invalid", "*").Result(),
+			ie:     collections.NewIncludesExcludes().Includes("ns1", "invalid", "*"),
+			namespaces: []*corev1.Namespace{
+				builder.ForNamespace("ns1").ObjectMeta(builder.WithLabels("name", "ns1")).Result(),
+				builder.ForNamespace("ns2").Result(),
+				builder.ForNamespace("ns3").Result(),
+			},
+			expectedTrackedNS: []string{"ns1"},
+		},
 	}
 
 	for _, tc := range tests {
diff --git a/pkg/controller/backup_controller.go b/pkg/controller/backup_controller.go
index 24f8e64b2a..989617722c 100644
--- a/pkg/controller/backup_controller.go
+++ b/pkg/controller/backup_controller.go
@@ -463,7 +463,7 @@ func (b *backupReconciler) prepareBackupRequest(backup *velerov1api.Backup, logg
 	}
 
 	// validate the included/excluded namespaces
-	for _, err := range b.validateNamespaceIncludesExcludes(request.Spec.IncludedNamespaces, request.Spec.ExcludedNamespaces) {
+	for _, err := range collections.ValidateNamespaceIncludesExcludes(request.Spec.IncludedNamespaces, request.Spec.ExcludedNamespaces) {
 		request.Status.ValidationErrors = append(request.Status.ValidationErrors, fmt.Sprintf("Invalid included/excluded namespace lists: %v", err))
 	}
 
@@ -586,24 +586,6 @@ func (b *backupReconciler) validateAndGetSnapshotLocations(backup *velerov1api.B
 	return providerLocations, nil
 }
 
-func (b *backupReconciler) validateNamespaceIncludesExcludes(includedNamespaces, excludedNamespaces []string) []error {
-	var errs []error
-	if errs = collections.ValidateNamespaceIncludesExcludes(includedNamespaces, excludedNamespaces); len(errs) > 0 {
-		return errs
-	}
-
-	namespace := &corev1api.Namespace{}
-	for _, name := range collections.NewIncludesExcludes().Includes(includedNamespaces...).GetIncludes() {
-		if name == "" || name == "*" {
-			continue
-		}
-		if err := b.kbClient.Get(context.Background(), kbclient.ObjectKey{Name: name}, namespace); err != nil {
-			errs = append(errs, err)
-		}
-	}
-	return errs
-}
-
 // runBackup runs and uploads a validated backup. Any error returned from this function
 // causes the backup to be Failed; if no error is returned, the backup's status's Errors
 // field is checked to see if the backup was a partial failure.
diff --git a/pkg/controller/backup_controller_test.go b/pkg/controller/backup_controller_test.go
index c89bdf3894..ad7677923d 100644
--- a/pkg/controller/backup_controller_test.go
+++ b/pkg/controller/backup_controller_test.go
@@ -190,16 +190,10 @@ func TestProcessBackupValidationFailures(t *testing.T) {
 		},
 		{
 			name:           "use old filter parameters and new filter parameters together",
-			backup:         defaultBackup().IncludeClusterResources(true).IncludedNamespaceScopedResources("Deployment").IncludedNamespaces("foo").Result(),
+			backup:         defaultBackup().IncludeClusterResources(true).IncludedNamespaceScopedResources("Deployment").IncludedNamespaces("default").Result(),
 			backupLocation: defaultBackupLocation,
 			expectedErrs:   []string{"include-resources, exclude-resources and include-cluster-resources are old filter parameters.\ninclude-cluster-scoped-resources, exclude-cluster-scoped-resources, include-namespace-scoped-resources and exclude-namespace-scoped-resources are new filter parameters.\nThey cannot be used together"},
 		},
-		{
-			name:           "nonexisting namespace",
-			backup:         defaultBackup().IncludedNamespaces("non-existing").Result(),
-			backupLocation: defaultBackupLocation,
-			expectedErrs:   []string{"Invalid included/excluded namespace lists: namespaces \"non-existing\" not found"},
-		},
 	}
 
 	for _, test := range tests {
@@ -214,11 +208,10 @@ func TestProcessBackupValidationFailures(t *testing.T) {
 			require.NoError(t, err)
 
 			var fakeClient kbclient.Client
-			namespace := builder.ForNamespace("foo").Result()
 			if test.backupLocation != nil {
-				fakeClient = velerotest.NewFakeControllerRuntimeClient(t, test.backupLocation, namespace)
+				fakeClient = velerotest.NewFakeControllerRuntimeClient(t, test.backupLocation)
 			} else {
-				fakeClient = velerotest.NewFakeControllerRuntimeClient(t, namespace)
+				fakeClient = velerotest.NewFakeControllerRuntimeClient(t)
 			}
 
 			c := &backupReconciler{
@@ -1574,43 +1567,6 @@ func TestValidateAndGetSnapshotLocations(t *testing.T) {
 	}
 }
 
-func TestValidateNamespaceIncludesExcludes(t *testing.T) {
-	namespace := builder.ForNamespace("default").Result()
-	reconciler := &backupReconciler{
-		kbClient: velerotest.NewFakeControllerRuntimeClient(t, namespace),
-	}
-
-	// empty string as includedNamespaces
-	includedNamespaces := []string{""}
-	excludedNamespaces := []string{"test"}
-	errs := reconciler.validateNamespaceIncludesExcludes(includedNamespaces, excludedNamespaces)
-	assert.Empty(t, errs)
-
-	// "*" as includedNamespaces
-	includedNamespaces = []string{"*"}
-	excludedNamespaces = []string{"test"}
-	errs = reconciler.validateNamespaceIncludesExcludes(includedNamespaces, excludedNamespaces)
-	assert.Empty(t, errs)
-
-	// invalid namespaces
-	includedNamespaces = []string{"1@#"}
-	excludedNamespaces = []string{"2@#"}
-	errs = reconciler.validateNamespaceIncludesExcludes(includedNamespaces, excludedNamespaces)
-	assert.Len(t, errs, 2)
-
-	// not exist namespaces
-	includedNamespaces = []string{"non-existing-namespace"}
-	excludedNamespaces = []string{}
-	errs = reconciler.validateNamespaceIncludesExcludes(includedNamespaces, excludedNamespaces)
-	assert.Len(t, errs, 1)
-
-	// valid namespaces
-	includedNamespaces = []string{"default"}
-	excludedNamespaces = []string{}
-	errs = reconciler.validateNamespaceIncludesExcludes(includedNamespaces, excludedNamespaces)
-	assert.Empty(t, errs)
-}
-
 // Test_getLastSuccessBySchedule verifies that the getLastSuccessBySchedule helper function correctly returns
 // the completion timestamp of the most recent completed backup for each schedule, including an entry for ad-hoc
 // or non-scheduled backups.