Eriksen was born 11 December 1927, in Oslo. His parents were Marius Eriksen (1886–1950) and Birgit Heien (1900–1996). Marius Eriksen competed in the 1912 Olympic Games as a gymnast. His brother, Marius Eriksen, Jr. (1922–2009), was an alpine skier and during World War II became a fighter ace in the Royal Norwegian Air Force. Stein Eriksen was the top slalom racer in Norway in 1949 and took bronze in the slalom at the 1950 World Championships in Aspen, Colorado.