No, this is a common urban myth. In fact, we use almost the whole of our brain over the course of a day. We probably only understand about 10% of how the brain functions which is where the myth might come from.
Hi smartiepants, butters, and kjelpke! It is not true. Since I was curious to learn more I looked it up. Here’s a cool article I found in SciAm by a brain-scientist who gets this question all the time. He has some interesting arguments as to why it can’t be true, so you may want to check it out: http://www.scientificamerican.com/article.cfm?id=do-we-really-use-only-10
Really great question!! I learned a lot from it! =)