The suspect was sentenced in 2015 by a Belgian court for his alleged role in an Islamist recruitment network.
A man convicted of terrorism in Belgium has been arrested trying to enter Bulgaria, authorities have said.
The suspect was detained on Wednesday during a special operation involving border police, the Bulgarian prosecutor's office said in a statement.
The man is wanted in connection with a "20-year prison sentence for terrorism" in another European country.
Prosecutors also said the suspect had been given a prison sentence of nine years and five months in Turkey on terrorism charges.
Bulgarian media have identified the man as Yassine Lachiri, who allegedly has ties to Abdelhamid Abaaoud, the mastermind of the November 2015 attacks in Paris.
A source close to the investigation confirmed to AFP that the man arrested in Bulgaria was Lachiri.
In 2015, he was sentenced in absentia by a Brussels court in a trial into an alleged Islamist recruitment network.
Meanwhile, the Belgian federal prosecutor's office said they were preparing an extradition order.
Paris is preparing to mark the sixth anniversary of the terror attacks that killed 130 people and injured dozens of others.
A landmark "trial of the century" into the November 2015 terror attacks is also underway in the French capital and is likely to run until May 2022.