do you need mountain lion in order to mirror macbook pro on apple TV

Welcome to the Apple Support Communities

You need OS X Mountain Lion to use AirPlay Mirroring if you have a compatible Mac > http://support.apple.com/kb/HT5404

If you don't want to upgrade to Mountain Lion or your Mac isn't compatible with AirPlay Mirroring, you can use a third-party application to stream your computer onto the Apple TV, as AirParrot > http://www.airparrot.com

Note that, if you upgrade to OS X Mountain Lion and your Mac isn't compatible with AirPlay Mirroring, you will have to use AirParrot to stream your computer onto your Apple TV

In your case, you can upgrade to Mountain Lion and use AirPlay Mirroring, or use AirParrot. I recommend you to upgrade to Mountain Lion and use AirPlay Mirroring because you will get more features