The multiple beam klystrons (MBK) offer some distinct advantages over their single beam versions including higher average power, relatively lower operating voltages, higher bandwidth and low individual beam current. In this paper the design of the radio frequency (RF) section of a multiple beam klystron working in the J band frequency range is presented. The RF design and simulation has been carried out using a commercially available three dimensional electromagnetic design code. A cold test model of the RF cavity has been fabricated and its resonant frequency has been characterized. Design of the individual cavities, simulation results of the beam wave interaction as well as the frequency characterization of the fabricated cavity is presented in this paper.