I'd be inclined to give the "check the fluid" thing a miss, low fluid would bring on another light. The ABS light should come on for ABS problems, BTW, the ABS system is checked automatically every time you start the car and "move away". You say its your first service, if the car is new or has some secondhand warranty, would this not cover fixing the ABS system? As said already, it is usually dirt/corrosion on one of the reluctor rings or a sensor - but get it checked/fixed anyway as no ABS in winter can be a bit of a
problem! Only other thing that springs to mind is a brake light pedal switch starting to play up - but I would have expected other lights to have come on as well. Also remember, if you force the ABS system to "work", it should not bring on the ABS fault warning light. A scan should reveal all (also as said already) everything else is speculation I'm afraid.