Ferdinand August Rojahn (1822-1900) was a German-born organist, violinist and conductor.
The son of Johan Friedrich Gottlieb Rojahn and Dorothe Philipine (Schünemann) Rojahn, he was violin and piano teacher to the Norwegian composer, violinist and conductor Sigurd Lie (born 1871).
Rojahn was a Stadmusikanten in Kristiansand, Norway. He was "orchestra leader" of Musikselskabet Harmonien (which later became the Bergen Philharmonic Orchestra) from 1856 until 1859. Rojahn was married to Birgitte Cornelia Gulbrandsen (1839-1927); they had 6 children.