That usually means it's broken....  ;-)

It helps if you say what kind of vehicle and it's mileage and age.
There are different things to look for on a newer vs older vehicles.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos:  Non members can still view!
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Basically the repair is done as follows:

Stuff all available space with twenty dollar bills and take it to the
dealer.  When the vehicle is returned the light and the bills will be
gone.

Seriously, ABS is not a problem that is fixable by someone w/o a bit of
training and/or experience, you really do need to see the dealer.

Year, model?

9 times out of ten it's a dirty ABS computer connector.

Remove it, clean it, replace it.
I use spray contact cleaner and remove the air filter to make a
little sink in which to work.
Plus put some dilectric grease on the connectors after your done.

it's a system on the vehicle thats need to have failure codes retrieved from
the abs computer then and only then can a  good diagnosis's be made guessing
just cost more money