A customer on Npower's standard tariff will benefit from a £35 reduction in their year bill, paying an average of £1,245.
The reduction will not come into effect until the end of March.
Npower increased its electricity prices by 14 per cent six months ago.
Kevin Miles, retail head of Npower, said: "We will continue to keep our costs and prices under review to ensure that we remain competitive and give our customers value for money."
Meanwhile, Npower has published a white paper called UK Climate Policy for Business, which highlights the financial benefits to be gained from cutting carbon emissions.
Click here to run an energy price comparison, and see if you could be paying less for your gas and electricity.