Mejia was claimed off waivers by the Angels on Thursday, Jeff Fletcher of The Orange County Register reports.
Mejia will head back to the Angels after a two-game, three-inning sojourn with St. Louis in which he allowed three earned runs. The 26-year-old appeared in four games with the Angels earlier this season before being DFA'd on July 26. He's currently out of minor-league options, so he's likely to get an extended look as the Halos assess his potential role on the squad next season.