Xion

It must be about three years old. It doesn't have a single problem besides what I called "sticky keys", for lack of a better term.
Whenever I play a game online involving the arrow keys/directional pad, I've encountered this problem constantly. I'll be minding my own business when suddenly, my game cursor/character/player will move in the direction of the key I had just pressed. The only way I've been able to stop this is by pressing the key again, but no matter what I do, it keeps occurring. How do I get rid of this?