Yes. Harry and Voldemort are related, however distantly. Harry is a decedent of one of the Peverell brothers (Ignotus I believe) and that is the reason he has the invisibility cloak. The Gaunts are also relatives of a different Peverell brother. Therefore, Harry and Voldemort do share a common ancestor. This relationship, however, is not thoroughly discussed in the book but can be concluded by reading the pieces about the Deathly Hallows and how Voldemort found the stone that brings people back to life in the Gaunt's ruined house.