Currently, you can’t prevent your lobbies from filling up with console players. Activision hasn’t confirmed when that feature will be available, but this space will keep you informed.
How to turn off crossplay in Call of Duty: Modern Warfare 2 for PC
How to turn off crossplay in Call of Duty: Modern Warfare 2 for Playstation
Upon hitting the main menu, look to the upper right of your screen for the icons for Home, Channels, Notifications, and Settings.
Then, go to settings and scroll down to Account and Network. Click it, and you should see ‘Crossplay’ listed at the top. If it’s green, click it, and Crossplay should be disabled. If it’s gray, it’s already disabled.