In this paper, a particular standard MicroGrid (MG) is accurately simulated in the presence of the Electric Vehicles (EVs) participating in decentralized primary frequency control service. It examines effect of number of the participating EVs on the short-term dynamic behaviour. The simulation results confirm that frequency deviation will not definitely become zero even though an unlimited number of the EVs participate. The output power of each EV is determined according to the frequency deviation. On the other hand, the output power of each EV affects the value of the frequency deviation, especially in small-scale MGs and MGs with predominant inductance behaviour. Eventually, an equilibrium point is reached after a new EV is added that depends on the characteristics of the MG and the functions executed in the MG central controller during such a service. Additionally, effect of Reflex method, an advanced charging technique for EVs, on the frequency deviation is examined.