It is the matter of jurisdiction of the country in which you live or cash out your Bitcoins. Since Bitcoin is not legal yet and hence not classified under forex or commodity trading, the tax rate for those activities won't apply for Bitcoin.

However, in my country, I pay tax for converting Bitcoins into the fiat currency but that applies to the transaction fee and not the transaction amount.

Unocoin | Fee Structure.

As per the current tax rate, it is 18% of the transaction fees in my case. However, when it comes to the income tax, I do have my investments in Tax savings schemes so I never cross the minimum taxable slab when it comes to the final income.