We study high-energy gamma-ray afterglow emission from gamma-ray bursts (GRBs) in the prior emission model, which is proposed to explain the plateau phase of the X-ray afterglow. This model predicts the high-energy gamma-ray emission when the prompt GRB photons from the main flow are up-scattered by relativistic electrons accelerated at the external shock due to the prior flow. The expected spectrum has the peak of ~10-100 GeV at around the end time of the plateau phase for typical GRBs, and high-energy gamma-rays from nearby and/or energetic GRBs can be detected by the current and future Cherenkov telescopes such as MAGIC, VERITAS, CTA and possibly Fermi. Multiwavelength observations by ground-based optical telescopes as well as Fermi and/or Swift satellites are important to constrain the model. Such external inverse-Compton emission may even lead to GeV-TeV gamma-ray signals with the delay time of ~10-100 s, only if the plateau phase is short lived. © 2010 The Authors. Journal compilation © 2009 RAS.