The 33-year-old 'Motivation' hitmaker confirmed the happy news via Instagram by posting a picture of Witherspoon's sports shoes alongside a matching baby pair, reported People magazine.
The photograph was accompanied with the caption, "I'll be stunting like my daddy."
Rowland first sparked rumours she is expecting when she and her husband, who is also her manager, were spotted shopping at upmarket baby store Bel Bambini in West Hollywood last month.
"They checked out the furniture and strollers on the second floor and walked around downstairs," a source said.
Rowland and Witherspoon got married in an intimate ceremony in Costa Rica last month.