The proposals, which will reportedly be unveiled in Lord Carter's Digital Britain report this month, recommend a tax on ads placed on sites such as , and .
The level of the proposed tax is not known, however it would come on top of corporation tax and VAT.
Ministers plan to use the money for rolling out broadband and to provide funds to state-owned broadcasters.
Channel 4 is forecasting an annual shortfall of £150m by 2012.
The online tax may force internet firms to start charging users for email, search or social networking services. Critics say the extra costs would be passed on to customers.
Another option being discussed is a tax on broadband providers based on the amount of data used by their customers.
The proposed taxes would need to be approved by the Treasury before they could be introduced.