Yes, a belief which relies on logical validity and self-consistency of memory and thought, which would in turn need to be the result of a "simulation". And by "need", I really mean "much more likely than the alternative" of producing such a state otherwise.
But are you really scanning all of your beliefs for consistency at every moment? Couldn't you just be presented with a simulated feeling that your beliefs are consistent? Wouldn't that be enough? It's certainly plausible that a Boltzmann brain could have that.