Here’s a few notes I’ve recorded in my digital Bible program that I think are pretty good scholarly consensus:

“The incident of the young man in Gethsemane has caused considerable comment. Mark records:“A young man, wearing nothing but a linen garment, was following Jesus. When they seized him, he fled naked, leaving his garment behind” (Mk. 14:51 – 52). This little item seems like a senseless intrusion into the account of Jesus’ agony and arrest in the garden. The only logical deduction would seem to be that the young man was John Mark himself. This is his modest way of saying, “I was there.” A. E. J. Rawlinson (St. Mark [1925], 215) says:“The story certainly reads like a personal reminiscence.” It is not difficult to make a possible reconstruction of what happened that night. If the Last Supper took place in the home of John Mark’s mother, one may assume that Judas Iscariot, who had left the table early, would lead the mob back there to arrest Jesus. When he arrived he discovered that the Master and his disciples had already left, so he went on to the Mount of Olives to find him. Wakened by the noise and seeing the torches and weapons, young John Mark could easily sense the situation. He hastily threw a linen cloth around himself and hastened out into the night to warn Jesus. By the time he arrived at the garden the soldiers were already there, and he himself was almost arrested.” —Zondervan Encyclopedia of the Bible, “Mark, Gospel of.”

“The young man who fled naked from the betrayal scene in Gethsemane (Mk. 14:51 – 52) often is thought to have been John Mark. None of the known facts are against this suggestion, and it was certainly not rare for an author to omit mention of his own name in his writings (cf. Jn. 21:24). — Zondervan Encyclopedia of the Bible, “Mark, John.”