No details regarding when they got engaged or whether they have set a wedding date were immediately available.
The couple met on the set of the soon-to-be-released film "Magic Mike" and have been dating for about six months, UsMagazine.com said.
Keough is the 22-year-old daughter of Presley's only child, singer-songwriter Lisa Marie Presley.
Pettyfer, 21, has appeared in the films "I Am Number Four," "Beastly" and "In Time."
Celebrity Breakups and divorces of 2014 [PHOTOS]