Aliens vs Predator demo recently popped up in the Spotlight section of the Xbox 360 dashboard. The ad reportedly announced that the demo will be released February 4, this Thursday. Unfortunately, the ad has since been pulled, though AvPGalaxy reports finding the ad as well.
The site also notes that the demo will arrive on the same day for PSN and Steam as well, adding that an official announcement from Sega is forthcoming. Given that the game will be hitting retail shelves in just two weeks, the timing for the demo would certainly make sense.
We'll be sure to update this post if and when Sega makes things official. Update: it's official!