By using a self-consistent particle-in-cell simulation we investigated the effect of driving frequency (27.12–70 MHz) on the electron energy distribution function (EEDF) and electron-sheath interaction in a low pressure (5 mTorr) capacitively coupled Ar discharge for a fixed discharge voltage. We observed a mode transition with driving frequency, changing the shape of EEDF from a strongly bi-Maxwellian at a driving frequency of 27.12 MHz, to a convex type distribution at an intermediate frequency, 50 MHz, and finally becomes a weak bi-Maxwellian at a higher driving frequency i.e. above 50 MHz. The transition is caused by the electric field transients which is of the order of electron plasma frequency caused by the energetic ‘beams’ of electrons ejected from near the sheath edge. Below the transition frequency, 50 MHz, these high energy electrons redistributes their energy with low energy electrons thereby increasing the effective electron temperature in the plasma, whereas, the plasma density remains nearly-constant. Above the transition frequency high-energy electrons are confined between opposite sheaths which increases the ionization probability and therefore the plasma density increases drastically.