There are no countries in Antarctica as such. Seven countries have claimed part of it but all have signed up to the Antarctic Treaty meaning that they have put aside their claims indefinitely. The seven countries are Chile, UK, Argentina, Norway, Australia, France and New Zealand. A host of other countries (including the USA) have acceded or ratified the Antarctic Treaty.
Whilst Antarctica is a continent, there are no individual countries contained within it. It's just a big, icy land mass. Unlike the Arctic, nobody lives in Antarctica (except for a few visiting researchers, etc).
If it already contained separate countries, the rest of the world wouldn't keep making claims to it. Several nearby countries (Australia, New Zealand, Argentina, Chile) have made claims on it, as well as some rather less nearby (UK, Norway, France).