Johnston, the father of Sarah Palin's grandson, plans to run for the office in Wasilla as part of a reality TV show.
He said on "Real Time with Bill Maher" Friday that he's been talking to residents about his candidacy and is working on building a platform, although he didn't offer specifics.
Palin, the Republican vice presidential nominee in 2008, served as mayor of Wasilla from 1996-2002. She was elected governor in 2006.
Johnston says the appearance on Maher's HBO show would be his last interview for a while.