That’s the claim Daniel Wallace made during his most recent debate with Bart Ehrman at UNC Chapel Hill. In his summary of the debate at Parchment and Pen, Wallace writes:
We have as many as eighteen second-century manuscripts (six of which were recently discovered and not yet catalogued) and a first-century manuscript of Mark’s Gospel! … Bart had explicitly said that our earliest copy of Mark was from c. 200 CE, but this is now incorrect. It’s from the first century. I mentioned these new manuscript finds and told the audience that a book will be published by E. J. Brill in about a year that gives all the data. … I noted that a world-class paleographer, whose qualifications are unimpeachable, was my source.”
Later he described the newly discovered manuscript as “just a small fragment.” Nevertheless, if this is a manuscript copy of Mark’s gospel, and if it can be reliably dated to the 1st century AD, this would be the greatest NT manuscript find to date, surpassing even p52 (a small portion of John’s Gospel, dated to ~125 AD)! We’ll have to wait and see.
UPDATE 2/16: Dr. Wallace has written specifically on this issue on the Dallas Theological Seminary website and added a tiny bit more information by saying “it was dated by one of the world’s leading paleographers. He said he was ‘certain’ that it was from the first century.” In the comments I have also quoted Dr. Ben Witherington III regarding the owner of the fragment, and a bit more detail about it. Witherington made it sound as if it is much more than a “small fragment.” I guess we’ll have to wait until next year to see how small is small.