Well, your question is not specific enough. Of course it's allowed. However, if you are based in Qatar and doing business in Qatar, you will need to set up an LLC to operate legally. This is a costly process, but I wouldn't recommend doing business in the public arena without the proper approvals.

However, if you are NOT based in Qatar, there is really nothing to stop you doing business online without setting up a legal entity. Your Qatar clients will pay online and you will ship their goods.

Hope that helps!!