Try this:
I don't know how to do this without "on error" but note that in the code below the "on error" works only within the "Set" (because the "On Error Goto 0") line which will not undercover other errors in the code.
Code:
Dim oTbl As Table
On Error Resume Next
Set oTbl = ActiveDocument.Tables(1)
On Error GoTo 0
If Not oTbl Is Nothing Then
Exists = "yes"
Else
Exists "No"
End If