The dependence of the resonance position of the central-ECH (c-ECH) on plasma behavior was investigated using a fast camera. When the resonance positions were higher, low frequency fluctuation of ~6kHz was observed and at the same time the diamagnetic signal decreased. Also, the same frequency fluctuation was observed in the potential signal by Au beam probe. On the other hand this low frequency fluctuation was not appeared when the resonance position was seemed to be on the axis of the plasma. These results indicate that the convective ExB drift instabilities may be induced due to the off-axis heating by c-ECH.