Clearly some people in this thread have no idea what they are talking about.
In most grad schools, any form of C (or worse) is considered a failing grade. I think the theory is that by the time you get to grad school, average (C) isn't good enough. But, honestly, they really could just scale the grad school grades to mean anything if they wanted to.
Getting a B+ is just fine. You are well within the acceptable A+ to B- range. In the end though, grades don't matter in grad school (the research and publications are what matter). Mine didn't even keep track of a GPA. All I had to do is make certain that I never got any C's or below. You too will likely NOT be given a GPA for grad school. You don't put it on resumes either. I suppose you could calculate one yourself, but your future employers would have nothing to compare it to since they don't have GPAs from other applicants with grad school degrees. It all comes down to the number and quality of papers you produce (or presentations, posters, etc).