There is a rubber grommet that may have fallen out of the brake pedal.. The brake light switch has a plunger that hits the grommet. If that grommet is gone then there will be nothing to depress the plunger on the switch which will make the lights stay on. Get a flashlight and look up your brake pedal and find the switch.. it should have at least 2 wires going to it. It will have a plunger on it and that plunger will rest against a grommet when the brake pedal is not depressed.. Make sure that grommet is still in place. It is a simple part to install and they car very inexpensive.. It will have to be purchased from the dealership. They usually are not available aftermarket.. Good luck
You can also order these online from several different sources if your not near a dealer. Here is the cheapest I found http://www.jegs.com/i/Dorman/326/74015/10002/-1?CAWELAID=1710624734&CAGPSPN=pla&catargetid=230006180000848540&cadevice=c&gclid=CLvc2ZrXkMECFdDm7AodSlsAlA
If that link doesn't work try this one. http://tinyurl.com/bkpad
This one is the same size even though its for honda worked in my Nissan pickup. Had to replace it yesterday.