I'm assuming you've already checked the brake master cylinder fluid level as a low fluid level will cause the light to be on all the time. if the fluid level is okay and the parking brake is released then the problem may be with a brake lamp.check your brake lights. that light usually indicates that a brake light bulb is burnt out. be sure to check the brake light above the rear shelf as well.i think you'll find you have a burnt out brake light bulb.hope that helps