A parallel three-dimensional electrostatic particle-in-cell Monte Carlo Collision (PIC-MCC) code using an unstructured tetrahedral mesh is developed and validated in this paper. Poisson's equation is discretized by a nodal finite element method using a linear interpolation function. Charged-particle motion is traced cell by cell using a leap-frog method and the Boris scheme. Code is validated using quasi-one-dimensional radiofrequency gas discharge by observing the bi-Maxwellian electron energy probability distribution function at low pressure. Parallel performance of the PIC code is tested using a three-dimensional radiofrequency gas discharge on a PC-cluster system. Results show that parallel efficiency of 83% can be achieved at 32 processors with dynamic domain decomposition.