The searches of eight houses were linked to returning jihadi fighters from Syria and separate from investigations into the Islamic State attacks in Paris in November 2015 and the bombings in Brussels in March last year, a statement said.
"No weapons or explosives were found. In all, seven persons were arrested and taken for questioning," it said.
Belgium is the EU country with the highest per capita number of fighters who have gone to wage jihad in Syria and Iraq, a figure estimated at 465.
Belgium has been on high alert since the Paris and Brussels attacks, with investigators believing they were planned and carried out by the same IS cell based in the Belgian capital.