Safari update message on my Mac, why is it there for four days?
This will work with any stuck update from the app store, btw, just change the names of the stuff to delete.

First thing to try: clear the app store updates folder at Macintosh HD/Library/Updates

Second thing to try: Open Terminal (Applications > Utilities > Terminal) and paste this: open $TMPDIR../C and in there, delete anything that has the name com.apple.appstore then do the same in Terminal with this command: open $TMPDIR../T

Third thing to try: Open Disk Utility (Same place as Terminal), select your hard drive and run Fix Permissions.

One of those should do it.