There are several ways to detect a keylogger on a mac, from simply reviewing the processes running on the computer to using a mac os spy detection program.

Step 1 Open the Activity Monitor to check for unknown process. This system tool will allow you to view the programs (processes) currently running on your computer.

Step 2 Check and Research any unfamiliar processes running in your “Activity Monitor.” Critical system processes sometimes have unrecognizable names, however, and keyloggers may have a name that sounds legitimate.

Step 3 Download and install a mac keylogger detector or another software firewall. This type of mac software alerts you when another program tries to connect to the Internet. It will detect a keylogger for mac before it sends information over the Internet, and allow you to block it.
http://www.keylogger-for-mac-os-x.com/how-to-detect-a-mac-keylogger.html
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