FK dont worry too much about it mine has been doing this for the past year!!!!!!!!
I cleaned all the brake light bulb connectors as JB says but it still does it but even when the light is on the ABS still works
On mine it seems to come on when theres a big temperature change http://www.alfaowner.com/forum/ubb/icons/icon19.gif ie raining one day and sunny the next it`ll be on from the moment i start up or i can be sat in traffic and it will come on or screaming down the road it makes no sense
If any one can come up with a cure let me know if not it just means i got two red lights permanantly on which i ignore the other being the seatbelt warning light as i never wear it