A capacitive arc with a peak frequency at 1-10 kHz is observed during impedance studies on proton exchange membrane (PEM) fuel cells when a shunt resistor is used for measuring the current. A few studies have reported this feature, but its cause has not been identified yet. In this work, correlations between the high frequency arc and the experimental setup are analyzed. Experimental results show that the high frequency arc is likely an experimental artifact caused by neglecting the frequency dependence of the shunt resistor. Methods to avoid this type of distortion and a simple correction procedure are presented.