In many houses, the electrical outlets or receptacles show an open ground in some rooms. At times , it is a problem with the earthing in the outlet, but some times there is a fault in the main ground connection in the house itself.
For each outlet where there is no earth, check if the ground wire connection to the outlet is fixed properly. In many older houses, there is no ground wire connection or the wire is loose. If there is a ground wire to the electrical outlet, the outlet itself can be replaced by an outlet with a ground wire connection.
If there is no groundwire, a grounding type receptacle can be installed and a wire can be run from the ground to the outlet. A ground rod can be installed separately or the ground wire can be run from any other outlet which is already grounded.