Probably not. That happens in vehicles where the top inlet of the radiator is not the highest point in the cooling system, but it is by what might as well be a mile in a '64 Dart (or any other old Mopar, or most any old car, for that matter), so not possible for air pockets to form. That's a newer-cars thing.
But even if it were an air pocket, it would cause the opposite of the OP's problem. Air surrounding the coolant temp sender will cause the gauge to read lower than it would if bathed in liquid/coolant. The engine would be showing symptoms of overheating with the gauge not near H.