Prostate brachytherapy with the radioactive nucleus cesium-131 was studied using the Monte Carlo code MCNP5. The sources of radiation were in the form of encapsulated grains called the seeds. The radiation dose rates from the radioactive sources were evaluated using the F4 tally. Both photons and electrons were transported from the prostate to other places in the body. The body depiction is a modified version of the ORNL phantom. Several values of the seeds’ activities and their numbers were considered. The doses were evaluated for the prostate and other places nearby, assuming the seeds to be the point sources. The effects of changing the seeds’ form of distribution inside the prostate and taking into account their geometrical construction are investigated. The period taken for delivering the prescribed dose was predicted. The results are found to be in good agreement with other estimations.