Yes. The Moleman aka Harvey Rupert Elder currently lives in the underground realm of Subterranea. He is the ruler of the Moloids and basically the ruler of much of Subterranea and the caverns of Monster Isle. it is said that he is planning to strike back at the outer world in numerous attempts to rule or humble the world that had rejected him.

From what we know of the earth now, this would only be possible if the creatures resided in the crust of the earth, which has a maximum thickness of 70km. Below the crust is a layer of magma, which is liquid molten rock and under this is the core. The mantle and core are almost definitely too hot for life, and it is highly unlikely that anything could live in the crust without us realising. Also if it did in the crust it would have no oxygen, light and the weight of the earth above it would crush any space, so the creatures would have to live in rocks.