He played Tier II Junior "A" for the Abbotsford Flyers in 1982-83 and then played college hockey for the Denver Pioneers from 1983 to 1986. Undrafted by any NHL team, Mathiasen signed as a free agent with the Pittsburgh Penguins in 1986 after his junior year.
Mathiasen spent the next three seasons in the Penguins' farm system, being called up for a total of 33 NHL games. He scored a goal and seven assists. He retired in 1988.
He made a brief comeback with the Fresno Falcons in 1994-95 and 1995-96.