It could always be a test of the game's companion website. A Sony representative informed Shacknews that "Guerrilla Games is currently testing a number of elements internally with Killzone 3 and further details will be available soon."
A beta test was conducted for Killzone 2 prior to that game's release and it stands to reason that Killzone 3 would be tested as well. It remains to be seen if a beta, if planned, will be one of the bonuses included with a PlayStation Plus subscription as one of the advertised features is priority betas.
The game, which will support PlayStation Move and stereoscopic 3D, is scheduled to be released in February 2011.