Can I airplay a movie from safari on my MacBook to Apple TV and still use the computer for something else at the same time?

Hi frogjt,

Welcome to the Apple Support Communities!

Great question! You can absolutely do this in OS X 10.9. The attached article explains how the process of using AirPlay with Apple TV to create a second display. Also, towards the bottom of the article there are instructions on how to set your Displays preferences on the computer to make sure the TV and MacBook Pro displays are set up the way you want them to be.

OS X: Using multiple displays in Mavericks

http://support.apple.com/kb/HT5891

Have a great day,

Joe