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Measurements of the dynamical electrical transport behavior are performed on electron-doped manganites La(0.4)Ca(0.6)(Mn(1-x) Ru (x) )O(3) (x=0 and 0.02). An undoped sample possesses a robust charge-ordered antiferromagnetic ground state, and only a positive resistivity relaxation can be observed. However, a low-temperature negative relaxation behavior arises after inducing a few ferromagnetic orders to the charge-ordered matrix by tiny Ru doping. We assigned this difference to the dynamical competition between ferromagnetic metallic and charge-ordered insulating phases. Consistently, for a doped sample, the crossover from positive to negative resistivity relaxation behavior ensues around T=115 K, which is just below the ferromagnetic Curie temperature.