Johnston, 20, and Bristol Palin, 19, recently confirmed they are engaged for a second time.
The Alaska natives previously planned to wed, but called it off shortly after the birth of their son Tripp in December 2008.
"There is a lot of public speculation that Bristol and Levi have signed up for a reality show about their relationship. They have not," Bristol Palin's representative told UsMagazine.com. "While several networks have pitched different concepts, Bristol has not agreed to participate in any show. Her focus remains on doing what is best for Tripp and her family."