The man named as Faycal C was arrested on Thursday.
At least half the victims died at the airport, the rest in an attack on the metro in suicide bombings.
The Islamic State (IS) has claimed responsibility for the attacks.
The BBC quoted authorities as saying that Zaventem – Brussels international airport – will not reopen before Tuesday.
Meanwhile a demonstration against the attacks, scheduled for Sunday in central Brussels, has been cancelled after a request from the authorities.
Organisers said people’s security was a top priority.
Belgian prosecutors said that Faycal C had been detained outside the prosecutor’s office in Brussels on Thursday. A search of his home had found no weapons.
Faycal C was charged with “participation in the activities of a terrorist group, terrorist murders and attempted terrorist murders,” a statement said.
It gave no further details and made no comment on Belgian media reports that he was the third man in an airport CCTV image that showed the two suicide bombers – Najim Laachraoui on the left, and Brahim el-Bakraoui.
Belgian media say the third man is Faycal Cheffou, a freelance journalist.