Mathias Erik Tjärnqvist (born April 15, 1979, in Umeå, Sweden) is a former professional ice hockey forward.

His older brother, Daniel Tjärnqvist, was a defenceman for Djurgårdens IF.

He currently serves as an assistant coach for Malmö Redhawks in the SHL.

During the 2004–05 NHL lockout, Tjärnqvist played with HV 71 in the Elitserien along with fellow NHL'ers Manny Malhotra, Jonathan Cheechoo, and Bryan McCabe.

On February 12, 2007, he was traded to the Phoenix Coyotes, along with a first round pick in the 2007 NHL Entry Draft, for Ladislav Nagy.