The That '70s Show co-stars began dating in April, 2012, months after Kutcher separated from his wife of six years, Demi Moore, but they have avoided commenting on the romance, preferring instead to keep the relationship out of the spotlight.
However, the actor decided to share an intimate moment between himself and Kunis online on Tuesday (10Dec13), when he uploaded an image of the pair locking lips in silhouette beneath a neon sign bearing the word 'Sun'.
The accompanying caption simply read: "Sunset nofilter (sic)".
The public display of affection comes three days after Kunis took Kutcher to her brother Michael's wedding in Florida last weekend (07Dec13).
Kutcher's divorce from Moore was finalised last month (Nov13).