Try this, I think it'll work for you.
Sub Convert_Macro()
'
'
Dim File_Names As Variant
Dim File_count As Integer
Dim Active_File_Name As String
Dim Counter As Integer
Dim File_Save_Name As Variant
File_Names = Application.GetOpenFilename(, , , , True)
Application.ScreenUpdating = False
Application.DisplayAlerts = False
File_count = UBound(File_Names)
Counter = 1
Do Until Counter > File_count
Active_File_Name = File_Names(Counter)
Workbooks.Open FileName:=Active_File_Name
Active_File_Name = ActiveWorkbook.Name
File_Save_Name = InStr(1, Active_File_Name, ".xls", 1) - 1
File_Save_Name = Mid(Active_File_Name, 1, File_Save_Name) & ".csv"
ActiveWorkbook.SaveAs FileName:=File_Save_Name, FileFormat:= _
xlCSV
ActiveWindow.Close
Counter = Counter + 1
Loop
Application.ScreenUpdating = True
Application.DisplayAlerts = True
End Sub