please check earth wire or clean bulb holder for not earthing
most probably because the brake light switch is stuck in the "on' position. The switch is most probably right under the dash on the drivers side connected to the brakes swing arm pedal.when you step on the brake,the arm moves and set the brake light on.
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?
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.
your brake pads could be worn out.
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.
the brake light switch is out of adjustment. Readjust the switch.