Ryan is divorced from actor Dennis Quaid. They have an 18-year-old son together. Several years ago, the actress also adopted a girl from China. She is now 6.
Mellencamp has been married three times and has five children.
People.com quoted an unnamed insider as saying Ryan has been dating Mellencamp for about seven weeks.
The source said the singer and his wife, Elaine, separated some time before Mellencamp began his romance with Ryan.