A photomixing-based frequency-hopping spread spectrum (FHSS) system is effective for future secure terahertz (THz) wireless communications. Conventional photomixing systems are typically composed of two lasers, which result in an increased system size and power consumption. To address this issue, we applied our proposed THz wave generation method, using a single wavelength-tunable laser, to the FHSS system. In the experiments, we successfully demonstrated a J-band (220–330 GHz) FHSS system with a frequency-hopped interval of 400 ns.