The rocker announced that he and wife Deanna are expecting a "double blessing" earlier this year.
The couple are already parents to son Griffin and daughter Hannah.
Speaking to fans in a video blog posted on his official website, he said: "Big news. Deanna and I are having a boy and a girl. We are very excited about that."
He added: "We do have names picked out but we're going to keep them to ourselves until further notice."
The twins were conceived through IVF and are being carried by a gestational surrogate after Deanna underwent a partial hysterectomy four years ago.