The electrostatic potential due to an electric dipole at an equatorial point is

The electrical potential of a dipole is given by,

 $\mathrm{V}=\frac{1}{4{\mathrm{\pi \epsilon }}_0}\frac{\mathrm{p}.\hat{\mathrm{r}}}{{\mathrm{r}}^2}$

At equatorial plane $\mathrm{\theta }=\mathrm{\pi }/2$, therefore, electric potential at any point in the equatorial plane of a dipole is zero.