An electromagnetic spring-based variable stiffness actuator is a new concept with the potential to change stiffness faster than mechanical springs can; however, its nonlinear elastic property is a challenge in actuator design. In this paper, the torque response of a custom-made electromagnetic spring was studied using a ramping force test and electromagnetic simulation. A two-zone linear region, from 0° to 2° and 2° to 6.5°, was observed and explained through magnetic flux simulation to provide insight into the fundamentals of the electromagnetic spring. An unusual impedance response was also noted from this regional linearity, appeared on a step gain in Bode plot of end-point impedance in a dynamic test.