The Mechanicus has the same belief, with the Omnissiah (Emperor) being the manifestation of Deus Mechanicus, the machine god. According to this belief the Emperor serves a Jesus role in that he's the physical semi-mortal manifestation of the greater deity.
I thought that was just sort of an excuse to prevent the Ecclesiarchy from having a fit. Isn't the Omnissiah the C'tan trapped under Mars? Or is it the Machine God and I'm just getting confused?
A small fraction of the leaders of the Mechanicus believe the Emperor is not the Omnissiah, most do. None actually know for certain what the Machine God really is but some of the doubters suspect the Emperor hid something on Mars and tricked them.
In the Crusade he arrived on Mars, fulfilled a prophecy and was accepted by the Fabricator General, and the bulk of the populace, of the time as the Omnissiah. Despite this some Tech Priests were very skeptical of him. Some did not believe in gods at all, others simply thought he was not the real one. The latter group sided with Horus in the Heresy and became the first Dark Mechanicus. Despite being beaten and destroyed their suspicions live on among the leaders of the Mechanicus that have access to their ancient records.
The Void Dragon is sealed on Mars, and
might be the Machine God, but it's presence is known only to two people at a time. It's warden and their guardian (unless somethings has happened I'm not aware of.) The same book that confirms this also reveals that all technical knowledge can be found in the Warp, so the Machine God could actually be a warp entity or not even exist.
EDIT: Just to clarify, the Omnissiah is supposed to be the incarnation of the Machine God, hence the word being derived from messiah, since it's another Jesus/God reference by the original designers. It may or may not be the Emperor, the Void Dragon or fake.