According to P-Stats (Player Stats Network), who tracked active Battlefield 4 players across all platforms, the PS4 has the most active BF4 players. This includes players on PC.
As we all know Battlefield has been known for being highly popular on PC since the the franchise launched almost 11 years ago, but it seems as though the tide could be turning. It's not unusual that the PC version of Battlefield in the past has always had the more active players. The game did offer a much better experience to PC players than players on the older generation platforms because their hardware could handle the full experience. 64 players, more vehicles, the works. With the next generation consoles however, being able to provide the full Battlefield experience, and much improved graphics, it seems as though things may be changing.
Of course this could have a lot to do with the problems that Battlefield 4 players have experienced on the PC that has caused many people to walk away from the game. All platforms have been affected by the bugs and issues, but I think that many of the once loyal Battlefield community on the PC have taken these issues much harder than console owners because this was "their" game.
DICE is hard at work on improving Battlefield 4 with the CTE (Community Test Environment), and should have a game changing patch launching in early September. Hopefully this will bring PC players, and players on all platforms back to the game and back to the Battlefield community.