Dear Sreekanth, the question is a little ambiguous. Let me go deep, first if you want to know  the electroactive area you should tested against an electrochemical probe for example ferricyanide, of course that polyaniline have at least two reductions/oxidations peaks  (if I not messing something.) But I guess you could try with other probes in order to calculate the electroactive area for that interface. On the other hand when you work with acid and make cyclic voltammetries you see the peaks of polyanilne and you can calculate the Ks and the amount specie inmobilized in your electrode with the integration of the peaks of reduction and oxidation. In any case I think that the most important thing is that you define the word "active" . ¿ Active in what solution?¿Against what probe? ¿As sensor? ¿How much species is on the electrode?

Well I expect it works or helps,

Greeatings

Dear Andres Arrocha

Thank you very much for your reply. I want to calculate the surface area of poly aniline deposited on a 1 cm2 GC electrode, which is active in acid solution. For example we usually calculate ESCA of Pt using Q of hydrogen UPD / 210 μC.cm-2. Is it something like this is possible in polianilne ?

If you want to calculate the Surface area, check the Aokí´s work. He have developed a kinetic model to explain the chronoamperometric response in electroactive polymers. The model predicts the chornoamperometric response in specific  experimental conditions. According with the model, the chronoamperometric current response depends of the layer thickness and the Surface área.