In the images the pair can be seen holding hands and cuddling up to each other.
Roberts joined the Channel 7 drama in 2017 and plays Willow Harris.
This isn't the first time Stewart has been linked to one of his co-stars.
The 42-year-old was dated fellow Summer Bay resident Isabella Giovinazzo in 2016.
Stewart was previously engaged to actress Jessica Marais. The Packed to the Rafters co-stars are parents to daughter Scout, 5.