Titanfall had its alpha test begin recently, which we figured meant a beta couldn't be too far behind. That date appears to be set now: for February 14. A European retailer seems to have leaked the date in some promotional materials.
French retailer Micromania put out posters advertising the beta running from February 14-19, spotted by Softpedia. Meanwhile, Respawn's Vince Zampella has tweeted word of an impending announcement, though he didn't use the word beta. "Yes, we will have an announcement soon," he said. "I'm sure no one can guess what it will be..."
Assuming the posters are legitimate, though, the dates could differ for North America. We'll update as more information becomes available.