Jennifer, 42, had recently been the subject of numerous pregnancy rumours, prompted when she was spotted wearing a series of loose-fitting tops while out and about.
CLICK ON PHOTOS TO ENLARGE
Jennifer Garner and her husband Ben Affleck
But her spokeswoman Meredith O’Sullivan has told People that the speculation is "not true".
Jennifer and Ben, 41, are already parents to Violet, eight, Seraphina, five and two-year-old Samuel.
The couple, who are devoted to their children, were married in a beach ceremony in June 2005.
Batman star Ben moved millions of viewers around the world when he spoke openly to his wife in his touching Best Picture acceptance speech at the 2013 Academy Awards.
Reports that Jennifer Garner is pregnant with her fourth child are "not true", her rep confirmed
After thanking the cast and crew of his winning film Argo, Ben turned to address Jennifer in the audience.
"Thank you for working on our marriage," he said. "It is work – but it's the best kind of work. There is no-one else I would ever work with."