Frans Mostaert was a Flemish Renaissance painter specializing in landscape paintings.

Frans Mostaert was born in Hulst. The early biographer Karel van Mander states in his early 1605 Schilder-boeck that Frans Mostaert was the son of a common painter, the twin brother of the painter Gillis Mostaert and the grandson of the painter Jan Mostaert. While his brother Gillis studied landscape painting with Jan Mandijn, Frans became a pupil of the landscape painter Herri met de Bles. Van Mander states that both brothers joined the Antwerp Guild of Saint Luke in 1555. This may be one of the many errors of van Mander since Frans received a registered pupil in 1553. It is therefore more likely that he became a master in the Guild earlier.

Frans Mostaert was the teacher of Jan Soens, Adriaen Rebbens and Bartholomeus Spranger. He died of the plague in Antwerp, after his new pupil Bartholomeus Spranger had been with him only for a few weeks.