A better description of what's happening would be much more helpful, but off the bat, sounds like a stuck key or something. Have you spilled anything on your keyboard lately?
If this is the case, not much more to do than replace the keyboard. I hope you're talking about a standalone keyboard, not the top case of a laptop. That would be a much more expensive fix.
You can maybe try cleaning it by spraying a rag with a bit of windex and wiping it down vigorously, but if that doesn't do it, sorry.