Mine does this occasionally (Mac OS X/Safari).
At first I thought the mouse had died but it's not that.
A massive housekeeping appeared to cure it but the problem returned.
Hitting the tab key or the arrows sometimes clears it.
Failing that, unplugging and replugging the keyboard violently and swearing can scare it into behaving.
If not, force quit and go away and do something more useful.
The pricessor will sulk for a while then make up its mind to do what you want.
Until the next time.