Despite some sites claiming otherwise, there is no Grand Theft Auto V beta running at the moment - if you see or hear otherwise, it's a scam. There's a lot of them too, though fortunately Rockstar has been targeting these nefarious sites and their creators with legal action - seeing many of them now redirect to the official GTA V website.
Early this year, Take Two, Rockstar's publisher, filed five complaints to the World Intellectual Property Organization over different GTA V Beta domain names and websites that purported to offer people access to a beta that simply doesn't exist. Some of these included getgtabeta.com, gtavbeta.net, gtavbeta,org and a slew of others.
These sites don't just pop up out of nowhere though, they try and hedge their credibility with Facebook groups filled with fake likes/friends and artwork ripped straight from trailers.
Of course Rockstar and Take Two aren't the only companies who've had to deal with these fake beta domains before. Microsoft had issues with Halo 4 last year with different websites offering early access. Those sites were quickly taken down too.