Normally the screen is flashing red when you or one of the members of your group is in combat.

But if you aggro a mob and go into a city but this mob still things your are in range but it can't get to you. Your screen will stay like this as some stupid mob out there is trying to get to you to hit you. Just log out and back in

Thanks! I have been wondering for awhile. I got killed trying to solo a broken ass anchor; and although the anchor was long gone my screen kept flashing. They really need to improve the status communication and quit pretending about this immersion crap.