The prefix "extra-" means, "outside, beyond", such that "extraterrestrial" means, "from beyond earth." Based on that definition, I say no.
That said, I do believe there is more than is known about living beings that are reported as "aliens". On Star Trek (the original), it used to begin by saying, "Space, the final frontier". I believe we know more about space than we know about what is under the waters of the earth; and I know we know more about space than we know about what is inside the earth. We live on the surface, while Osama bin Laden lives in caves that only a few people know exist. There could be a whole other world of beings living IN earth. Underwater and inside the earth are still frontiers of our planet, still unknowns. If there are people in amazing flying saucers, I think there is a much higher percentage of probability that they come from an ancient earth civilization, which went underground 10,000 years ago, but make day trips to the surface for some needed essentials. The time it would take to reach earth, coming from the closest star (other than our Sun), would take light years of travel (thus some spaceship with "warp drive"), and that makes that possibility prohibitive. The average American worker would piddle away a whole afternoon on the Internet, if left unsupervised. Imagine what having a light year or two, being cooped up inside some hunka hunka flying metal, without direct connection to the home planet would do.
Ask me about "interterrestrials".