The general consensus at languageandgrammar.com is that the expression general consensus is redundant.
Consensus means that the majority holds the same opinion; in other words, it’s the general opinion of the group. Logically, then, not only is there no reason to use the word general in front of consensus, but it’s an error of redundancy–unless saying general general opinion does not seem redundant to you to you.
Language redundancy is a common problem in English. Part of the reason for the redundancy issue–I mean, problem (No, I’m never going to let that go, so don’t ask me to)–is a tendency to repeat what we’ve heard before rather than think about what we’re saying. We’ve heard general consensus hundreds or thousands of times, so we don’t question the validity of the two words when combined; thus, we repeat the redundancy.
I talk more about redundancy in my book; in fact, one chapter in Literally, the Best Language Book Ever is devoted to redundancy and repetition.
Paul’s book–Literally, the Best Language Book Ever