The singer revealed the news in a video posted on YouTube and announced she would be continuing her world tour.
The baby boy has been named Eissa.
It is the first child for the singer and her husband Wissam Al Mana.
The sister of Michael Jackson looked gleeful in a Facebook video announcing her and her husband's plans.
Janet Jackson has denied reports that she has throat cancer after cancelling her concert tour.
Janet Jackson has quashed rumours she is planning to marry billionaire Wissam Al Mana - by announcing they're already married.