The children will be the first for the couple, who married in 2008.
"In order for my wife and I to have our life, we need to be up front and I need to be able to share things with you and be real," UsMagazine.com reported Cannon said on his 92.3 Now radio show Thursday.
"I didn't even tell my wife I was gonna do this," he added. "I'm probably gonna get yelled at for not getting permission ... We are having twins!"
The 41-year-old singer and her 30-year-old husband confirmed the pregnancy in October, but offered few details about it at the time.