If there's nothing wrong it wouldn't be on. If it's the red brake light, that turns on if the parking brake is not fully released, there' unequal pressures in the two hydraulic circuits, or the brake fluid level is low in the reservoir. Low fluid will make the light flash randomly, not at a steady rate. If the fluid is low, do not fill it. It is low either because there's a leak or the front disc brake pads are worn out. That means it's time to have the brake system inspected.