I'm seeing this same problem with a brand new MS Natural Elite via PS/2. Older keyboards of the same type have the same issue. Strange thing is that if I just ignore the error, I can manage the bios just fine. Windows XP works just fine too. This is the latest bios - tygr110h.86a.0037.2009.1216.331. This looks like a bios issue and it sure would be nice if it got fixed.
I don't suppose the anoying beeping will ever get changed.