And just in case you want to count chart sheets as well, with a slight tweak on Jason's code:-
Sub Count_WS()
Dim a As Integer
a = ActiveWorkbook.Worksheets.Count
b = ActiveWorkbook.Charts.Count
MsgBox a & " Worksheets, " & b & " Chart Sheets"
End Sub
or if you wanted it all lumped together, including any chart sheets
Sub Count_WS()
Dim a As Integer
a = ActiveWorkbook.Sheets.Count
MsgBox a & " Sheets"
End Sub