In my post, Acts 3:19-21 and the Book of Mormon, I addressed an argument against the Book of Mormon which stated that, according to Acts 3:19-21, Jesus would never leave heaven until the Second Coming, so His post-ascension appearance to the Book of Mormon peoples contradicts the Bible. In this post, I discussed Acts 23:11, which explicitly states that Jesus appeared to Paul, post-ascension:
And the night following the Lord stood by him, and said, Be of good cheer, Paul: for as thou hast testified of me in Jerusalem, so must thou bear witness also at Rome.
The following are just representative comments on Acts 23:11, showing that this was a physical appearance of Jesus to the apostle Paul and not a metaphorical "standing" of Jesus beside Paul:
11. The following night the Lord stood at Paul’s side and said, “Keep up your courage! In a dream during the night after his being returned to Roman custody, Paul again sees the risen Kyrios (recall 18:9), who appears to him and encourages him in his trial. The Lord stands by him, as did Ananias (22:13), as a measure of support. (Joseph A. Fitzmyer, The Acts of the Apostles: A New Translation with Introduction and Commentary [AB 31; Garden City, N.Y.: Doubleday, 1998], 730)
Paul’s worst apprehensions of what might happen to him at Jerusalem looked like being fulfilled. Where now were his plans for carrying the gospel to the far west, and visiting Rome on the way? He might well have been dejected and despondent after the events of these two days. But on the night following the abortive appearance before the Sanhedrin, the risen Lord appeared to him as He had done at critical moments before, and bade him cheer up: he had borne witness to Him in Jerusalem (a reference this, no doubt, to this speech at the top of the steps to the crowd in the temple court), and he would live to bear witness similarly in Rome. This assurance meant much to Paul during the delays and anxieties of the next two years, and goes far to account for the cam and dignified bearing which seemed to mark him out as a master of events rather than their victim. (F.F. Bruce, The Book of Acts [The New International Commentary on the New Testament; Grand Rapids, Mich.: Eerdmans, 1977], 455)
11) Up to this time Paul had had only the divine intimation that he would be bound (a prisoner) and placed into the hands of Gentiles in Jerusalem, and this prophecy had been fulfilled. Now further light falls on his path.
Now on the following night the Lord, having stepped up to him, said: Continue to be of good cheer! For as thou didst testify the things concerning me in Jerusalem, so it is necessary for thee to testify also in Rome.
The present imperative need not imply that Paul was downhearted. It was not because “Paul never needed Jesus more than now” that the Lord appeared to him, ἐπιστάς, came suddenly upon him. This was only the second night of his confinement, and he was the last man to lose courage quickly. The Lord is now adding more light of prophecy and doing so not through others but in his own person. The imperative θάρσει, “continue to be of good cheer (comfort, courage),” looks forward to the long imprisonment ahead of Paul. A spirit, as full of energy as his, might not hold up under such long inactivity as the weary months dragged along, and the clouds did not once lift. The Lord is fortifying him in advance for that. He would very often lean on what the Lord himself now reveals to him. (Lenski, R. C. H. (1961). The Interpretation of the Acts of the Apostles (p. 940). Minneapolis, MN: Augsburg Publishing House.)