Current–voltage (I–V) relations of Nd_0.5 (Ca, Sr) _0.5MnO₃ are investigated near its percolationthreshold. Resistivity and I–V relations reveal the unstable nature of Nd_0.5 (Ca,Sr)_0.5 MnO₃. A large slope change in the I–V curve is observable for low (I<15 mA) applied current by manipulating the applied magnetic field at 85 K. Our results indicate that the external applied current can assist not only an insulator to metal transition but also a metal to insulator transition.