This event occurred in the Garden of Gethsemane the night Jesus was betrayed and captured. Mark 14:51–52 describes a young man who, wearing only a linen cloth, followed Jesus. When he was seized by the Roman soldiers, he escaped capture and ran, leaving the garment behind. The identity of the man is unknown, but since the Gospel of Mark is the only gospel that mentions the incident, many Bible scholars speculate that the young man was John Mark himself, the author of the Gospel of Mark.
It is impossible to know for sure who the young man was, since the Bible does not specifically identify him. There are all sorts of explanations and supposed hidden spiritual/allegorical meanings on the young man who fled naked. None of them have any explicit biblical support. But we understand that the identity of the young man who fled naked must have had meaning to the original readers of the Gospel of Mark. The identity that makes the most sense, with that in mind, is John Mark.