I realize this is an old question, but I found this forum on accident and wanted to reply in case anybody else has this same problem. This is a very common issue on the 1998-2002 Accords.
I am assuming the light is usually on in the morning (or cold start) and goes out after a bit. Remove the cap, slide the float up toward the cap and see if the light goes out. If this is the case, replace the reservoir screen inside the brake master cylinder. We sell the part at my dealership for about $7. Simply pull the old screen out and drop the new screen in. Voila!
What causes this? Brake fluid naturally absorbs moisture (and should be flushed every three years, or when moisture is visibly present). This moisture turns into a green-looking goop that clogs the screen. With the screen clogged, the fluid stays low inside (above) the screen, and the sensor thinks you are low on fluid. Replacing the screen will allow the fluid to return through it; in turn, lifting the float back up.
Hope this helps.