Open Question: why in the world does this happen!?

on my laptop sometimes when im playing a game where you have to use the arrows on any game site the controls mess up. like when i press right the arrow key pops back up but the character keeps moving right and to make him stop i have to press the right key again! this happens on every game on every website. it used to not happen. my computer got boring because of this! how do i make it stop! it does not happen on my other computer though.