People.com said wedding-bell buzz began after the "Hitchcock" and "Cat on a Hot Tin Roof" star was seen wearing a pear-shaped diamond ring in New York Monday.
"Scarlett is absolutely not engaged," her publicist told People.com Wednesday.
Johansson was married to actor Ryan Reynolds for two years before they divorced in 2010.
Reynolds has since married actress Blake Lively.
Celebrity Families of 2014 [PHOTOS]