Christians believe that Jesus is in Heaven with God, until He decides to send Jesus to Earth for the final judgement. This event is known as the Parousia.

and stood before Him while Jesus was on the Christ and entrusted the care of Mary to John. Following the ascension, John may have wound up in Ephesus, and had among his pupils Polycarp of Smyrna.

This same Jesus, who has been taken from you into heaven, will come back in the same way you have seen him go into heaven.’ ...