A queueing system of two queues with exponential service time is considered. Customers arrive at each queue in each Poisson process. They observe the queue on arrivals and they determine whether to move to the other queue. The decision is made without observing the other queue. A threshold policy which includes some probabilistic behavior of the customers is assumed to determine the customers' behavior. The steady state probability under threshold policies of the customers is calculated by numerical method. Nash equilibriums of the threshold policies are analyzed through the numerical results.