There are two brake lights. One says BRAKES and basically indicates hydraulic or parking brake problems. The other is the circle with marks around it, which indicates excessive pad wear on the front brakes.
If it is the circle with marks, you either have a wear sensor contacting the rotor, or one of the leads has shorted to ground. If the BRAKE light is coming on, you have a hydraulic situation or possibly the switch on the parking brake foot pedal assembly.