I assume that the receptacle is standard 3-prong and "Open Ground" was read from a plug in outlet tester.
What you can do is remove the outlet and check the ground connections. Sometimes the grounding wire is wrapped around a screw on the box and not to the receptacle and the installer assumed the ears of the outlets would make a good enough ground contact with the box. Although not likely, this can defeat the ground over the years. What is more likely is if there is an insulator between the ears and the receptacle. Then simply remove the insulation. If that grounding conductor is long enough then you can attach it to the green screw of the outlet -- the right way of doing it. If there is not enough wire then an electrician should be called for giving you options if you really need to use that outlet.