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.

Heaven that had been closed to men before the Resurrection now at the Ascension was opened by Christ the Savior. The Ascension of Our Lord Jesus Christ. Greece. XVI century None of the righteous men ...

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.