Update: Looks like the site address for the beta got out a bit early.
Respawn head honcho Vince Zampella tweeted the following earlier tonight regarding the upcoming Titanfall beta:
Tonight at 6pm PST there will be a website to sign up for #titanfall beta access. The website will be announced shortly before 6.— Vince Zampella (@VinceZampella) February 11, 2014
We'll let you know more when we know more but I would be sure to follow the official TitanFall twitter account if you aren't already.