Is my macbook unibody discharging electricity?

It's normal.

If your mains power is 230 V you are more likely to perceive the sensation you describe than if your mains is 115 V. The sensation can be annoying but it's harmless.

There is a grounding problem if this phenomenon occurs. I would hardly consider it "normal." No two humans have the exactly same resistance. What is a tingle to you could be a shock to me. A properly grounded system should not produce electrical sensations in the person touching it. This should be the case regardless of the mains voltage.

Call an electrician and have the ground integrity of your house checked. Tingling with the 2 pin should stop with the 3 pin plug.

The charger came with an extension line that has a 3-pronged plug on one end and a duck-head on the other. Could try using it.

I have tried using both two pin and three pin sockets and I can feel vibrations

I guess that may not mean that he tried the 3 pin plug as well 🙂

Vibrations aren't that important. It's feeling electricity that is. The vibrations may be caused by the transformer inside the charger. The core may be vibrating slightly. I've not taken one apart, but I'm guessing they use a switching power supply with a high-frequency transformer.

Kappy wrote:

There is a grounding problem if this phenomenon occurs.

Grounding is irrelevant since the MacBook's case is not grounded.

Correct, they do, and many people describe the tingling sensation of ac current as vibration. Semantics aside, if there was no change between a 3 pin connection and a 2 pin something is wrong. No ground, possibly reversed live/neutral, possibly with a ground/neutral bond at the service entrance.

I'd call sparky. 🙂

Read my new post, call an electrician.

No, but there is always a ground side to power lines. The case itself is ground. A bad capacitor or resistor can cause the flow of electricity through the case to the individual and from the individual to his/her ground point.

This can happen within the case or within the power adaptor. They should not occur because they can be potentially dangerous.

Kappy wrote:

Vibrations aren't that important. It's feeling electricity that is. The vibrations may be caused by the transformer inside the charger.

Feeling is irrelevant as well, there are no (mechanical) vibrations, and the tiny transformer within the switching power supply operates in the high KHz range.

If the OP is concerned he should definitely consult Apple, or an electrician, or both.

The case is not "ground". A MacBook's case does not require grounding. None of the many international safety standards Apple complies with requires it. The case is capacitively coupled to the mains through the power adapter, which results in the sensation the OP described.

The case voltage can be as much as 115 V to ground if your mains power is 230 V. However, the capacitance is such that the available current is well within acceptable limits and harmless to you and your Mac. Measure it yourself if you like.

This power adapter design is typical of nearly all consumer electronic products and facilitates EMI requirements.

Is it potentially dangerous? Absolutely, if the power adapter is counterfeit, this is one of the many shortcuts cheap knockoff manufacturers take, and is the reason for Apple's recent counterfeit adapter trade-in program. A properly designed and constructed power supply may have about a millimeter of air insulation between the mains power and you. Tolerances are obviously critical. A counterfeit adapter may easily exceed them.