It's real, but probably not what you think if your idea of necromancy comes from role-playing games. It's not about resurrecting the dead, or animating skeletons or LARPing.
In real life, necromancy is nothing other than mediumship. It's contacting souls of dead people, usually to get answers or comfort people who lost their loved ones. And this was called necromancy since ancient Greece and the Catholic church still calls it necromancy and forbids it.