The couple posted a video on YouTube announcing the happy news. A.J. said to the camera, "I just wanted to say thank you, guys, for all your love and support… we want to share something special with you. We're having a baby!"
McLean, 34, then appeared on stage Sunday night at the Backstreet Boys with New Kids on the Block concert in London, showing off the back of his t-shirt which had "Daddy-to-Be" written in glitter.
The couple tied the knot in early December.
Backstreet Boy A.J. McLean and makeup artist wife Rochelle Karidis announced they are expecting their first child.