Is the Antichrist already alive on earth?
We do know that there is one who is coming to deceive and will be the antithesis of all that is good and Christ-like. The Bible indicates that this man will be sent by Satan to lead the world in a final rebellion and "will oppose and will exalt himself over everything that is called God or is worshipped ... proclaiming himself to be God" (2 Thessalonians 2:3-4).
Your question is a valid one because the events of the world, as they relate to the fulfillment of prophecy should cause every believer to keep watch. It is true that there has never been a time in history in which the world was as ready as it is now to usher in the end. Is he alive today? It is very likely he is alive right now.
The most important thing is to place your trust in Jesus Christ, alone. He will reveal to you everything that you need to know in His timing. If you are not a Christian, you will face horrible things unless you place your hope and trust in Jesus Christ. You can do that today by saying a simple prayer asking Jesus to forgive you for your sins, repent and ask Him to come into your life and be your Savior.