If the brake warning lights comes on and off while driving, the possible reason is that that the brake fluid is low. There is a sensor located on the top of the fluid reservoir that causes the brake warning light to go on when the brake fluid level is below minimum.

Brake Fluid Image Credit

When the Fluid is slightly low or below the minimum requirement there is still a tendency that the fluid touches the sensor especially when the car runs on a humps or a dip which causes the fluid to touch the sensor which resulted warning light coming on and off, because the fluid will slosh to the sensor.

Possible cause of brake warning light that comes on and off

Brake fluid level is slightly low.

How to fix brake warning lights that comes on and off

To fix this problem you have to add enough amount of brake fluid on the reservoir. A high quality brake fluid will do, usually DOT3 or DOT 4. When adding amount of brake fluid never leave the reservoir open for a longer period because it can cause the brake fluid to become contaminated with moisture coming from the air and may cause more problems. Also never allow the brake fluid to make contact with the painted surface of your car because only an small amount of brake fluid can damage your car.