Modified Newtonian dynamics is a major competitor of dark matter theory and contains not only a gravitational constant but also an acceleration constant. Based on a circular orbit solution for a two-body problem, this paper is devoted to studying a plane circular restricted three-body problem using modified Newtonian dynamics. We work out the Lagrangian points and the Hill curves akin to those observed in Newtonian dynamics. In contrast, however, the location and number of Lagrangian points, as well as the profile of the Hill region, are dependent on both the acceleration constant and the mass ratio of the main celestial bodies. These findings reveal a new avenue for testing modified Newtonian dynamics.