Keys, 33, and Beatz, whose real name is Kasseem Dean, welcomed baby Genesis last weekend, reported the New York Daily News.
"The joy of joy is joy!!" she captioned a photo on Instagram of the baby's footprints.
"We are so grateful! #blessings!," she added.
The 'Girl on Fire' singer and Beatz have been married since 2010 and are also the parents to four-year-old Egypt Daoud.
He is also the father to three other children from previous relationships - Prince Nasir, 14, Kasseem Jr, seven, and six-year-old Nicole.