Welcome to the Apple Community.
If you don't want to use a remote with your computer the easiest thing to do is just to turn the IR off. (System Preferences > Security > General, click on the Advanced button in the bottom right corner - If the button is greyed out, click on the lock icon and enter your administrators password))
If you still want to use your computer remote then you must pair your computers remote with the computer AND the Apple TV remote with the Apple TV.
To pair a remote with a device hold down the menu and FF buttons together for six seconds or until you see a chain icon on screen (best take the computer into another room, or turn it off, when you do this)