"Happy birthday America, more good news," McConaughey said in a blog posting Wednesday. "Camila and I are expecting our 3rd child, God bless, just keep liven."
He did not reveal the baby's gender or anticipated birth date.
The "Magic Mike" star married Alves, a model from Brazil, last month. They began dating in 2006 and are the parents of a 3-year-old son and 2-year daughter.