The 29-year-old man, born in Angola, was apprehended while trying to sneak aboard a passenger plane operated by Angolan airline TAAG, the Correio da Manha newspaper said.
Another daily, Diario de Noticias, said the suspect admitted to having spent time early this year in a Syrian training camp run by Islamic extremists.
He has not said what he intended to do on board the plane, and a judge ordered him to be held in custody, both newspapers reported.