Authorities revealed that the detained individual was the leader of Sharia4Belgium, Fouad Belkacem.
"We have indications that Sharia4Belgium was sending people to Syria to join terrorist groups there," Reuters quoted a spokesperson for Belgium's federal prosecutors as saying.
Prosecutors had declined to confirm whether anyone else has been arrested.
Sharia4Belgium is known as a Salafist group opposed to Syria’s President Assad.
Foreign insurgents have been playing an increasing role in Syria’s civil war that began in March 2011 with street protests against the rule of Assad. Belgian authorities became concerned after it was reported that about 80 Belgians joined opposition fighters in Syria.
According to the latest study, hundreds of European Muslims have joined the Syrian rebels in their fight against the regime.