I'm assuming you are using a Roku TV. No, you have to hit the Home button, return to the Roku home screen, then select Live TV.
If you're using a Roku player, you can certainly change the TV input to something else without returning to the home screen. Just be aware that the Roku will continue streaming if you had something playing, even if you aren't watching it. If you have an Internet cap, that might be a bad thing.
Dan Roku Stick (3600), Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.