World Bulletin / News Desk
Police raided eight addresses in the Brussels districts of Molenbeek, Schaerbeek, Anderlecht and Laeken.
Since deadly terror attacks in Paris in November 2015 and in Brussels in March last year, the country has been on high alert with police and soldiers enforcing tight security measures.
However, Tuesday's raids were not related to those attacks but to find people suspected of having gone to fight in Syria and Iraq, the prosecutor's office said in a statement.
No weapons or explosives were found during the raids.
Belgium is known for having a high number of foreign fighters. The country has designated 611 of its nationals as foreign fighters or people who went to Syria or Iraq and returned or who have planned on doing so.