Unfortunately:
"As of 1/14/2014, Evenbalance.com (the developers for Punkbuster) have fully dropped support for Call of Duty 4 (PC and Mac). The pbsetup.app will no longer work or update for Call of Duty 4. If you receive punkbuster errors within the game, you will need to turn the punkbuster option off within the game."
Source:
http://support.aspyr.com/entries/22015006-PunkBuster-Update-problems-with-COD-4-
On a bright note, it isn't just a Mac thing. Windows users are going to need to shut it off as well I think unless everyone sticks with whatever the last update to it was I guess?