Recently, fluoroscopy using computed tomography (CT) has gained significant attention. This is largely driven by the clinical application of the CT fluoroscope (CTF) is guided biopsy. Many studies have been conducted for the optimal presentation of the information. Little attention has been paid, however, to the temporal response of the CTF. The temporal response is important in understanding the inherent limitations of the CTF and in determining the best guided biopsy procedures. For example, during the biopsy operation, when needle is inserted at a relatively high speed, the true needle position will not be correctly reflected in the displayed fluoroscopy image until sometime later. This could result in an overshot or misplacement of the biopsy needle. In this paper, we perform detailed analysis of the temporal response of the CTF. We first derive a set of equations to describe the average location of a moving object observed by the CTF system. The accuracy of the equations is verified by computer simulations and experiments. We then show that the CT reconstruction process acts as a low pass filter to the motion function. For a general weighting function used in the tomographic reconstruction process, the impact on the observed needle motion depends on the biopsy needle location, the needle motion orientation and speed, and the weighting function itself. As a result, there is an inherent time delay in the CTF process to the true biopsy needle motion and location. This analysis can be used as a useful tool in the optimization of the biopsy procedure parameters. It can also be used as a guidance to the biopsy operator during training.