Chabi Yayi, son of former Beninese president and current opposition figure Thomas Boni Yayi, was arrested early Sunday at his home, according to several of his relatives.
No reason was given for the arrest which comes a week after a foiled coup attempt.
"At this time, we don't know what he is accused of," one relative told AFP.
"We don't know if it is linked to the events of last Sunday," said another close friend, a member of the Democrats party, the main opposition party, which Yahi heads.
Thomas Boni Yayi condemned the abortive coup in a video address, two days later.
Several arrests have taken place since the December 7 putsch attempt, including several participants and the former minister of defence and key opposition figure Candide Azannai, who was placed in police custody for "conspiracy against the authority of the State and incitement to rebellion".
Benin has also issued an international arrest warrant against pan-Africanist and anti-Western influencer Kemi Seba.
Several of those who staged the failed coup, including their leader Lieutenant Colonel Pascal Tigri, remain at large.
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