Are Ereada® mats grounded?

Yes, all Korean mats are grounded, they have a special net of wires in the charcoal layer to catch e-waves and forward them to the ground pin of the wall socket. 

It is not so important for modern EMF free heating system but it is preferable to have some contact with the earth when you lie on the mat. We lack it due to wearing rubber boots or sneakers. The mat provides grounding.