The illusionist's new Channel 4 show Apocalypse features Brown attempting to convince Steve Brosnan that the world had been struck by a meteorite, and that zombies had taken over.
Brown described the 21-year-old as having a "dead-end job", and that he was "stuck in a rut".
However, fans have claimed that Brosnan may be a stooge, after it was allegedly discovered that he belonged to a professional actors' casting website.
Brosnan's Twitter account was said to have been linked to his page on the Casting Call Pro site, but was later altered to the names Craig Harwood and Jerrin Matthews, before being taken down.
However, Channel 4 has since denied any reports that Brosnan has ever been an actor, and that the Casting Call Pro page was likely a fake.
A spokesman told The Sun: "Steven is not and never has been a professional actor. He was chosen purely because he fitted the characteristics needed for the show."
Derren Brown: Apocalypse concludes on Friday, November 2 at 9pm on Channel 4.