I know it sounds stupid, but are you sure the brake lever is all the way down? Just to see if the light is caused by that switch.
When you say its fine, how close to the full mark is it? I had that problem with the light on and it was due to my brake pads being too low. Changed the pads and all was well.
You might have some air in the lines or something is funky with the ABS module... I dont have ABS so Im not too sure why that light would come on.
Has this been on for a while? Does it ever go out? Did something happen before they came on? Any other info you have would be helpful...