Police searched 14 properties across the city and took the suspects for "thorough questioning", the federal prosecutor's office said.
The arrests were "within the framework of the inquiry" into the attacks on Zavantem Airport and the Maalbeek metro station in which 32 people were killed and more than 200 injured, the prosecutor's office said in statement.
"The investigative judge shall decide in the next few hours on their possible further detention," it said.
The Brussels suicide bombings, which were claimed by the Islamic State group, were carried out by a jihadist cell that was also behind the November 2015 terror attacks in Paris.
Tuesday's arrests come just four days after the brother of Oussama Atar, the fugitive suspected plotter of the Paris and Brussels attacks, was charged with leadership of a terrorist group.
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