Error analysis of electromagnetic motion tracking systems is of growing interest to many researchers. Under sensor movement, it is logical to presume that the error in position and orientation measurements will increase due to the linearization used in the algorithms, among other reasons. In this article, we analyze theoretically the error, that results from linearization, in position measurement of the Polhemus tracking system for a moving sensor. We derive formulas to estimate this error in terms of the sensor position and speed. Then, we verify these formulas by numerical simulations.