Naughty Dog is known for going months without divulging even the tiniest scrap of information about its games, and it's not that uncommon for one of the studio's projects to remain a secret for years. For instance, The Last of Us was actually developed alongside Uncharted 3, but was kept a secret for two years while the other game was being finished.
Gamers were in a similar situation recently: Naughty Dog announced that it had two major projects in development, but refused to tell fans anything about said projects. Eventually, it was revealed that one of the projects was the third Uncharted sequel, but the other project remained a mystery. With all eyes on Uncharted 4, it's likely that an official announcement about the second project is still a very longs ways off.
However, the secret may already be out. As pointed out by Gamespot, a former Naughty Dog employee may have spilled the beans on a sequel to The Last of Us:
Of course, the listing has since been removed, but it'd certainly be strange for one of Naughty Dog's senior animators to be wrong or inaccurate about which projects are in development. If The Last of Us 2 is indeed in development, then Knowland would have been one of the first people to begin working on it. If a lesser employee had listed it, such sequel rumors would be easy to ignore; when the news is coming from one of the higher-ups, it's far more likely to be true.
The Last of Us, when it was first released, was one of the few games that didn't immediately set up a sequel. The story closed in a way that didn't necessarily leave itself open, and while the game sold extremely well, many fans simply assumed that a follow-up wasn't going to happen. Even the game's creative director, Neil Druckmann, was torn on whether or not the game would ever receive a sequel.
With Uncharted 4 now standing in the spotlight, it's highly unlikely that fans will see anything official on The Last of Us for some time. That being said, it looks like gamers already know what Naughty Dog's up to, and could just be a matter of time before players head back into Joel and Ellie's world.
