Teacher Eco's answer is generally true for English language teachers. But there are exceptions to this. A teacher in elementary school or even high school will probably want the students to call him Mr. / Ms. / Mrs. X. And I think some university professors are very proud and want to be called Professor X, even the young English ones. You can ask him and find out for sure. Just say, "Excuse me, what should I call you? Professor X? Or...?"

No,it's not rude to call your teacher by his name,if he is from England and is not older than 60,I can assure you that he will even prefer that. That is the way how people talk to each other very common in English!