Are there electric outlets or wall switches anywhere? If so and they are flush with the paneling then it's probably a wall frame of 2x4s to give the depth and mount locations for the electrical boxes.
Difficult to remove, no, unless you want to do it non-destructive to the paneling, though I'm assuming the use of tiny finishing nails that will probably pull through the paneling when you try to pry it up.
Maybe after all this time the nails come out easily enough to not do damage, so what is the context of your question? If looking at a home for sale, you can't start tearing the walls apart, lol. Maybe an inspector can get away with that but a prospecitive buyer, isn't going to get approval from the average seller.