The verb "to rave about something/someone" generally carries a positive connotation, meaning to praise enthusiastically. For example, in the sentence "The critics are raving about that new film," it implies that the critics are expressing strong approval and excitement about the film.
However, the verb "to rave" can also mean to speak wildly or incoherently, often due to anger or madness, which is where the confusion arises. In most contexts, though, when used with "about," it refers to enthusiastic praise. So yes, the meaning depends on the context, but in the case of praising something, it is usually positive.