No. A helmet will not protect you from concussions. A helmet can cushion your skull, and help protect against skull fractures, but it cannot prevent your brain from moving within your skull. It is the movement of the brain within the skull that causes a concussion or other traumatic brain injury. A concussion actually creates a brain injury in two places.
The first injury happens at the initial point of impact and then a second injury occurs again on the opposite side as the brain rebounds away from the impact site. Regardless, it is still important to wear a helmet, especially one that fits properly and provides sufficient cushioning, when participating in any sports with a potential for head injuries.