In simple harmonic motion, when the displacement is minimum then 

Wkt,$\text{KE}=\frac{1}{2}\text{m}{\omega }^2\left({\text{A}}^{\text{2}}-y^2\right)$

At mean position, displacement is minimum (y = 0)

            $\text{KE}=\frac{1}{2}\text{m}{\omega }^2{\text{A}}^{\text{2}}\left(\max \right)$

and $\text{P.E}=2{\pi }^2{\text{mn}}^{\text{2}}\text{y}$

=0(minimum)