With the Call of Duty: Modern Warfare Open Alpha on PlayStation 4, Infinity Ward enabled the ability for players to connect their keyboard and mouse and play Call of Duty: Modern Warfare through the Alpha. For this Alpha, it does appears that keyboard/mouse and controller players are in mixed lobbies for testing as it is just an Alpha on platform.
Source: N4G PC Infinity Ward to add additional mouse and keyboard settings to PS4 version Modern Warfare