Welcome to AF.
The brake warning light serves at least 3 purposes. 1) Inform you of a hydraulic related problem with the braking system; 2) Indicate low level brake fluid at the master cylinder reservoir; and 3) When the emergency brake is engaged.
Any problem with the brakes should be checked into as soon as possible. To start check the master cylinder fluid level and check emergency brake operation. The emergency brake has a switch that may go bad.
Also, if you have ABS braking is the ABS light on or off?