The "Hitchcock" actress is three months pregnant and she is due in April, reported Ace Showbiz.
The 32-year-old actress apparently kept mum because she has had trouble getting pregnant in the past.
"Jessica has had tense times in the past when it comes to having a baby. So it is not surprising that she is staying mum on confirming the news publicly yet."
Biel and Timberlake, who tied the knot in October 2012 at the Borgo Egnazia resort in Fasano, Italy, celebrated their two-year anniversary while vacationing in New Zealand earlier this month.