According to SWTOR's Twitter, the test has been scheduled for November 25th through the 28th. This represents the largest beta test for the soon-to-be-released title yet, with hundreds of thousands -- perhaps millions -- of players invited to stress-test the servers.
The test might not technically be "open" beta, but it's pretty hard at this point not to get into it. Any player who registered for beta testing prior to November 11th is automatically included, and those that didn't can grab one of the thousands and thousands of keys floating out there -- including from us!
If you have questions about the beta test, it might behoove you to check out SWTOR's FAQ on the event.