Key presses inside Minecraft affect other programs

So this isn't just a Minecraft problem, this happens to a lot of other softwares I use on my computer as well. The problem is, when I press a key in Minecraft, even if it is in Fulscreen Mode, it will affect outside Minecraft, and its really annoying when you wanna focus on the game. So is there any program or anything that would kinda isolate Minecraft. Often I can't press some keys because it would send the keystroke to some other program instead of Minecraft. I use Linux Mint (19 I think). Thanks for spending your time to help me.