The emergence of mobile ad hoc sensor networks has brought new challenges to traditional network design. This paper compares the performance of two distributed computing paradigms, the client/server-based paradigm and the mobile-agent-based paradigm, through mathematical modeling and simulation. Previous works have shown that the mobile-agent-based paradigm is more appropriate to handle computations in ad hoc sensor networks. However, no simulation work has been done to quantitatively measure the performance. This paper first describes how computing is accomplished in the mobile-agent-based paradigm. It then presents a modified mathematical model and uses the execution time as a metric to measure the performance. Eight experiments are designed to show the effect of different parameters to the performance of the paradigms. Experimental results show that in the context of mobile ad hoc sensor networks with hundreds or even thousands of nodes, unreliable communication links, and reduced bandwidth, the mobile-agent-based computing provides solutions to low network latency and reliable data processing.