The bout, which was first reported by the Las Vegas Review-Journal, will headline 'The Ultimate Fighter 17 Finale' and take place in Las Vegas at the Hard Rock Hotel and Casino.
The announcement comes a little more than two weeks after Johnson (17-2-1) successfully defended his 125-pound title with a unanimous decision against John Dodson on Jan. 26 in Chicago.
Moraga (13-1) gets a title shot in just his third appearance on a UFC card. He is currently ranked sixth among flyweights by ESPN.com, and fourth by UFC.com.
In his most recent fight, on Dec. 29, Moraga submitted Chris Cariaso by guillotine choke in the third round at UFC 155.