I haven't heard of a virus that targets your keyboard, the whole idea is to try and keep a low profile so the user isn't aware of an infection. Whilst it may be possible if a true virus injected code into the keyboard driver file, inadvertently corrupting it. But that kind of file infecter would be targeting hundreds of files.
Other than the keyboard issue what makes you think that you have a 'virus' infection, e.g. have you any security software actually alerting ?
What is the type of connection on this keyboard, wireless, usb, ps2 ?
Have you tried a different keyboard ?