It is unlikely to have a significant effect, if robot's body is electrically conductive. Hitting the robot will just cause the electrons to travel along it's body to be grounded (either into ground or it just may fly off the robot and continue its travel). If sustained long enough, ie. if the charged particles themselves caused the robot's body to heat up sufficiently for the electrical conductance of the body at the point of the impact to drop below the threshold necessary for electron beam to propagate inside, it could do some damage, but at this point, it is more efficient to use other technology, to damage the chassis(laser, kinetic projectiles ...) and only once the internal parts are exposed, use the electron beam (however at this point you can just keep using what you have been using to get inside, bullet will damage CPU as well as electron beam).
HOWEVER, once electron beam can strike a semiconductor, it becomes exceedingly effective, as it can immediately damage the PN junction beyond recovery. And I think, one part of the robot's body would be exceedingly vulnerable to this sort of attack: It's cameras. Cameras are essentially an arrays of circuits, which if struck by high energy electron beam, would likely be destroyed and require replacement. This I find feasible in effect.
However, as others have pointed out, straight electron beam of any practical length is technologically immensely hard to generate. Closest analogues can be find in TVs and electron microscopes, where near perfect vacuum is maintained, in order to allow the beam to move unimpeded. But given high enough energy, it could work at some distances.
Word of the caution though, what you get is essentially a beta radiation gun, you really should not use it around people.