They named the suspect only as 35-year-old Y.A., giving no further details. Two others -- Abderrahmane A. and Rabah M. -- are also being held in Belgium over the same plot.
The main plot suspect is Reda Kriket, who was arrested near Paris last week after police found an arsenal of weapons and explosives at his home.
Y.A. is the third person to be charged in Belgium in connection with the plot. The others have been named as Rabah N. and Abderrahmane A.
The latter is known to be Abderrahmane Ameroud, who was convicted in 2005 by a Paris court for having played a role in the assassination of Afghan resistance commander Ahmad Shah Massoud.
Another man, Anis Bahri, was arrested in Rotterdam on March 27 at the request of French police and is expected to be extradited to France.