Value-Added Tax or VAT is considered to be a form of sales tax. The government imposes VAT only on services, physical goods, and barter exchange or lease of goods in a country. The question on whether or not your sales of bitcoins should be under the scope of VAT is out of the question as bitcoin does not seem to be a tangible product neither to be a form of service.
However, depending upon the laws stipulated in your country, cryptocurrencies in general may be subject to a special kind of tax specifically catering to that aspect only. It is still better that you make research or ask legal advices from lawyers in your country in order to avoid any conflict or anything whatsoever.
It is your duty and obligation to be aware of your current tax laws and that is why I heavily consider that you do your thorough research on the subject matter.