A spokesman said the suspect had telephoned Hasna Aitboulachen, the cousin of ringleader Abdelhamid Abaaoud, several times after the November 13 attacks and before a police raid five days later in which they both died.
A statement later identified the man as Abdoullah C., a Belgian national born in 1985, who was arrested on Tuesday on charges of “terrorist murders and participation in the activities of a terrorist organisation.”
The attacks and the Belgian links to them have shocked the country and sparked a sharp increase in visible security, with armed police and soldiers patrolling the streets in Brussels.
The police are especially looking for Brussels-born Salah Abdeslam, 26, who is believed to have fled from Paris back to the Belgian capital the day after the attacks on bars, restaurants, a concert hall and the national stadium left 130 dead.
A source close to the investigation told AFP last week that Abdeslam, who is believed to have played a key role in the Paris attacks, had got through three police checks as friends drove him from Paris.
Several people have since been charged with helping Abdeslam on his return to Brussels where he lived in the gritty Moelenbeek district, along with several others implicated in the attacks and extremist Islamist groups.
The Paris attacks were claimed by the Islamic State jihadist group.