Near's real name was kept a secret until the very end of the series when Mikami say it with the Shinigami Eyes. By that time Mello was already dead and it was stated that no one knew his name. Near on the other hand may have known Mello's real name as Light and the others found it out when Light's father say it with his Shinigami Eyes. The chances that Light would let that information slip into Near's hands is slim to none but the others probably told Near after the investigation ended.