http://en.wikipedia.org/wiki/Operation_Overlord As seen here. I can't seem to find anything about them being directly involved but I'm very curious and I'm hoping anyone here could specifically tell me if they all came at a later time.
No, the 1st Belgian Infantry Brigade, was not used in the Normandy landings (this disappointed them) because the British wanted the unit to be used in the liberation of Belgium. The government in exile did ask the British government to use the brigade in battle and the British complied, sending the brigade into action in France where they were under the overall command of the first Canadian army.
However, there were some Belgians who were put into a parachute unit who were air dropped into Normandy.
Edit: Should also add their was a commando unit made up of multiple nationalities of which Belgium was one.