Excel - Sacar promedio en una columnas cada 3 celdas, sin contar los 0

Sub CalcularPromedio()

    On Error Resume Next

    For Celda = 1 To ActiveSheet.UsedRange.SpecialCells(xlCellTypeLastCell).Row

        If Cells(Celda, 1) > 0 Then

           Suma = IIf(Cont < 3, (Suma + Cells(Celda, 1)), Cells(Celda, 1))

           Cont = IIf(Cont < 3, (Cont + 1), 1)

           If Cont = 3 Then Cells(Celda, 2) = Suma / Cont

           Pos = Celda

        End If

    Next

    If Cont < 3 Then Cells(Pos, 2) = Suma / Cont

End Sub