How does the charge of an electron differs from when it is at rest ?

You have confused two important concepts. Let's answer the question first. Charge does not change due to motion. It is a fundamental property of the electron.

The formula E = mc^2 is a statement that mass and energy are really the same thing. One can beconverted to the other. Charge on the other hand is a different fundamental property an does not have a relation simlar to mass and energy.

Now one of the posts put up the equation for the effective mass of a particle as a function of speed. This is a relativistic effect and if you work through the physics (which is not the same as writing an equation), you find that the mass increases with speed by converting some of the energy that would have goen to kinetic energy into mass. But charge does not change.

The Charge doesn't change, but small particles such as electrons change their mass when accelerated according to the equation-:

Reletivistic Mass = Rest Mass / (1 - (sqrt(speed of electron / speed of light))

See this link....

http://en.wikipedia.org/wiki/Charge_invariance

Charge is not affected by velocity.

Mass is...

m(rel) = m(rest)/SQRT[ 1-(v/c)^2]