Prinsloo shared a photo of herself in a bikini, displaying a her pregnant stomach.
She captioned it "ROUND 2..."
The couple's daughter, Dusty Rose, was born Sept. 21, 2016.
After Levine, 38, and Prinsloo, 28, married in 2014, the singer said in an interview that he wanted to have "100 kids" with her.
The pregnancy comes in the middle of a very busy time for the Maroon Five frontman: he's gearing up for the premiere of the new season of "The Voice," his band just released a new single, "What Lovers Do," and they plan to release a new album in November.
Maroon 5 has two shows in Brazil on Thursday and Saturday.