Keyboard types wrong characters J=5 etc. VERY STRANGE!

I've been a mac user for 7 or so years now and I've never had a problem like this:

I am on my PowerBook G4 which I have had for 6 months now and just this past week the keyboard started acting up. About once every other day or so when I am typing what comes up on the screen is not even close to what I typed. I'll hit H-E-L-L-O and 5-*-4-3-2 or something like that will come up. When I restart, the problem goes away for a few minutes to a few days. So I think it is software related and not hardware.

Has anyone had similar issues or have an idea how to solve so I don't have to keep restarting?

is it possible that num lock is on (F6 key and dim green light behind letters)? The letters also dub as a number pad. You could also have a glitch in the system, but check num lock first.