Both are correct, but you would only come across the 'of' version in older texts - novels, songs and poems from at least fifty years ago. It sounds elegant and literary to the modern ear. In modern English, we say 'about'.

Hi Hamed, "Everybody is talking about him" is a better choice. Both "about" and "of" are prepositions, but "of" is typically used to express the relation of one object to another, or one part of an object to the whole. For example, you could say "The window is part of the car". You could also say "Hamed lives to the east of me." The preposition "about" is used to indicate a subject. For example, "I thought about answering this question." It is also used in UK English slang to mean moving or location. "He walked about the town square." You may hear people from the UK and Australia use "about" in this manner.