In contrast to the extensive study of domain reversal in ferromagnetic materials, the domain switching process in antiferromagnets is much less studied due to the difficulty of probing antiferromagnetic spins. Using a combination of hysteresis loop, Kerr microscope, and x-ray magnetic linear dichroism measurements, we investigated the antiferromagnetic (AFM) domain switching process in single crystalline Fe/CoO bilayers on MgO(001). We demonstrate that the CoO AFM switching is a Kolmogorov-Avrami process in which the thermal activation energy creates AFM domain nucleation centers which further expand by domain wall propagation. From the temperature- and thickness-dependent measurements, we are able to retrieve quantitatively the important parameter of the CoO AFM activation energy, which is shown to increase linearly with CoO thickness.