The minister, who was not identified, was attacked yesterday in Ipanema, the tourist division of the civil police said in a statement.
A 26-year-old man was arrested along the beach front and the victim's belongings were returned to him, the statement said.
Globo news' G1 site reported that Portuguese Education Minister Tiago Brandao Rodrigues was assaulted at knife point and forced to hand over his money and cellphone. The Portuguese embassy in Brasilia did not respond immediately for comment.