Post-quantum cryptography (PQC) algorithms were introduced in response to the threats of attacks using quantum computers. The CRYSTALS-Kyber and CRYSTALS-Dilithium are two of the algorithms chosen by NIST to standardize the PQC, which are lattice-based algorithms. Number theoretic transform (NTT) helps lattice-based algorithms reduce latency, but it is still their bottleneck. Along with that, the RISC-V instruction set architecture also opens up flexible methods to solve different problems. This paper proposes a RISC-V system-on-a-chip (SoC) architecture with a computational accelerator for NTT-based calculations for Kyber and Dilithium. Implementation results show that software running on proposed SoC using accelerators has improved in NTT/INTT by up to 36.75×/42.69× compared to software on embedded devices, up to 4.07×/4.38× for software running on RISC-V SoCs, and up to 8.11× for NTT of the previous software/hardware architectures.