Private Sub CommandButton5_Click()
Dim deger As String, m As Integer
If ListBox1.ListIndex = -1 Then   'If there is no item selected on listbox,no move will be made.
MsgBox "Choose an listbox item from left", , ""
Exit Sub
End If

deger = ListBox1.Value
For m = 0 To ListBox2.ListCount - 1
    If deger = CStr(ListBox2.List(m)) Then
        MsgBox "This item already exists in ListBox2", vbCritical, ""
    Exit Sub
    End If
Next
ListBox2.ListIndex = -1
 ListBox2.AddItem ListBox1.Value
ListBox1.RemoveItem (ListBox1.ListIndex)
Call animation_to_right
End Sub 

Source