brake warning light on can mean your handbrake is engaged or that brake fuild is low. Those would be the first two easy things to check. If your brake fluid is low, you will need to keep a close eye on that, as you may have a leak and that can lead to a loss of your brakes.
...I have the exact same problem with my 1993 corolla.......Brake System warning light and discharge warning light
brake light switch would be most common cause
The most likely cause is low-brake fluid.
More than likely it is the brake light switch that is attached to the brake pedal.
Is it the parking brake light or the ABS light? is it red light or amber?
i would heck that you have the correct double element bulbs in your tail light assembly
It is possible that a wheel speed sensor is bad. This will cause the anti lock braking to not read the wheel correctly which would be a brake problem that would cause a light.
A short in the brake light circuit.
i would try changing your bulb in the rear of the car first then if it still not working then look for fuse or wiring problem
Low brake fluid, pads worn down, other problems.
short circuits in the turn signal and brake light circuits
On your brake peddle there is a switch it is either bad or stuck, most likely.