Before calling GoBack, the CanGoBack property can be inspected to determine whether there are entries in back navigation history.

The following example navigates to the most recent entry in back navigation history, if one exists.

Private Sub backButton_Click(ByVal sender As Object, ByVal e As RoutedEventArgs)
    If Me.NavigationService.CanGoBack Then
        Me.NavigationService.GoBack()
    End If
End Sub

void backButton_Click(object sender, RoutedEventArgs e)
{
    if (this.NavigationService.CanGoBack)
    {
        this.NavigationService.GoBack();
    }
}

.NET Framework

.NET Framework Client Profile

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference