Rudi Garcia's side sit second in Serie A with just one defeat in seven games, having suffered a controversial 3-2 reverse to champions and current leaders Juventus earlier this month.
Roma started their Group E campaign with an impressive 5-1 win over CSKA Moscow before claiming a deserved 1-1 draw at Manchester City.
That leaves them two points behind Bayern and Robben is anticipating a tough test at the Stadio Olimpico on Tuesday.
"Roma are our toughest rivals at the moment," he said. "They're playing the best football in Italy at the present time."
Team-mate Thomas Muller scored the winner in Bayern's 1-0 triumph in Moscow last time out, with the hosts having put a heavy emphasis on frustrating the Bundesliga champions in that game.
"Especially as a forward, you relish playing a team who are unlikely to pull all 11 men back to their own penalty area," said Muller.
