I'm guessing you have a cMBP, so you need to turn off your infrared receiver on your mac. Go to System Preferences, click Security & Privacy, then click General, then click Advanced and disable IR.
or you could pair the remote exclusively with your apple tv (it won't work with your mbp until you unpair it again)
on the remote press and hold the Menu and Right buttons for 6 seconds.
or, in your apple tv's main menu, go to
Settings > General > Remotes
- Pair Apple Remote.
I had the very same problem. As soon as I pressed play on my apple tb, iTunes would start playing. This proved quite useful since I hadn't realised I had a remote for my mac... Handy when plugging my mac to the tv to watching movies.