If you get this error when you turn your computer on you can rule out any virus (unless it's an bios virus but that's highly unlikely).

If you checked your keyboard on an other machine and it works fine there, it's not the keyboard.

Try to hookup another keyboard to the computer that gives you the error. If it still gives a keyboard error the most probable cause is a defective ps/2 port. It could also be you exchanged the mouse and keyboard connections.