The 30-year-old actress was spotted shopping earlier today wearing a diamond band on her ring finger, reported E! Online.
The couple are apparently planning to make it official soon.
Kunis and Kutcher, 36, began dating in 2012 after his split from former wife Demi Moore.
The 'Two and a Half Men' star and Moore, got separated in 2011, after being married for six years, amid rumours that Kutcher cheated on Moore.