Bioware has announced that the next Mass Effect game is in production, but we won't be seeing it for another two years or so.
In an interview with Gamer Syndrome, a Bioware employee revealed some news about the next installment in the Mass Effect franchise. The employee stated that the next game is most likely looking at a release sometime between late 2014 and mid 2015. They went on to reveal that full time production on the new game started about a month or two back.
Bioware made it no secret that we would receive more Mass Effect games; revealing almost immediately after the trilogy ended that the universe they'd created would be a waste to just throw away, and that there would indeed be another sequel. Bioware made it pretty clear though, that Mass Effect's protagonist, Commander Shepard, would not be featured in any major way.
A while back, the developers reached out to the fans to ask for their input on whether the new game should be a sequel or prequel, and while the majority of gamers seemed to indicate they wanted the story to pick up in the aftermath of Mass Effect 3, we have no definitive knowledge so far, of what the game will contain.