I have come across this problem, which I have never had before. It came across all of the sudden, I didn't even Install/Download anything that could have triggered it.
When I am typing, whatever key that it decides it wants to trigger itself, will be "stuck" and repeat. It has happened to me 3 times even while typing this. While this "stuck" event is happening, I can't press anything else on the keyboard, only clicking.
I have a Microsoft Wired 600, quite a plain and simple keyboard that I have had for 3 months. Here is a screenshot I took when it happened to me.