I was graded unfairly on a group project We had a group project that involved 4 people. 3 of us worked really hard. Personally, I feel I did about 1/2 the work. We had a Viva at the end of the project. I got nervous and did quite badly. When the grades were out I got a B, same as the guy who didn't really do much. I'm wondering if it's a good idea to ask the professor to consider re-evaluating my grade.
It is a good idea to ask. But you probably won't get a change in grade. 

The "ask", however, should be about why the grade is lower than you thought it should be. Learn, if you don't already know, what the grading criteria was and how much each element contributed. The professor should be able and willing to answer these sorts of questions. 

But it should also have been clear before the project started what the grading criteria should be and how important would be the evaluation of each part. It is possible that half the grade was assigned on the presentation. 

Learning what happened gives you the chance to work on those things in which you were judged lower than the others. That is the real reason for asking.

If you really want the grade changed then get your teammates to advocate for it based on your contribution to the other part. But that will have to come from them, not just your claim of doing "half".