The representative told People magazine exclusively the boy's name is Jack.
"He arrived earlier than expected and will be spending some time in the NICU [neonatal intensive care unit]," the statement said. "The happy parents thank you for your warm wishes and ask that you honor their privacy during this time."
Faris, 35, and Pratt, 33, were married in 2009.
Faris has had roles in movies such as "The Dictator," "The Hot Chick" and the "Scary Movie" series.
Pratt stars on the television situation comedy "Parks and Recreation."