Path independence of electrostatic potential energy changes.
Like gravitational systems, potential energy and kinetic energy also interconverts within electrostatic systems, although you need to be careful as to whether the MCAT passage refers to an ideal or approximately ideal system before you apply strict conservation of energy.
In other words, the passage may make it clear whether or not dissipation of energy through electromagnetic radiation is occuring, in which case the system may be losing energy to its environment as radiation.
Nevertheless, as with gravitational systems, it is absolutely true that the electrostatic potential energy depends on the relative position of the charges, not the specific path through which the charges have moved in the past. However, a change within a purely electromagnetic system may not be completely reversible due to emission of radiation. This is a somewhat advanced point really, and the MCAT would be probably give you some clues to coax you to think along these lines.