Resistive probe can detect the variation of electric field from a media by its current variation. Equivalently it is a variable resistor, which is sensitive to electric field. However, the experimental results show that another mechanism is involved in it and it is considered to have a relationship with the topography of the media. In this paper, this newly observed mechanism is explained as thermal effect with simulation results. This can affect the signal quality as a noise source or detection limitation of the field variation or, in other hand can be used as a highly localized thermal tip sensor.