Actually, I'm sure there is a way, as long as a person has access to the computer. There's probably some type of software used by corporations to monitor employee computer usage. In addition, searched MacUpdate for "keystroke logger" does come up with a utility called logkext. So of course it can be logged. Now, installing and monitoring it remotely might be difficult though. Securing physical access to your computer (i.e. setting up a password to come back from screensaver or sleep) would be the primary concern. You could also use Little Snitch to monitor apps making network connections.
I'm not aware of any way to "secure keystrokes" though.