The independent supplier blamed the rise on an increase in wholesale commodity costs in both gas and electricity.
Customers on the Better Energy pay monthly tariff will experience an average increase of £31 per year effective from 23 August.
Earlier this year the supplier hiked prices by 7.6 per cent for the same tariff.
Ovo said it reviews its prices on a regular basis and has a “strong track record of cost-reflective pricing”.
“These principles sit at the heart of the company’s promise to customers that the deal they are getting from Ovo will always be fair, transparent and as competitive as possible,” it said.
The firm claimed that, since June 2016, the forward price of gas and electricity have both increased by 8 per cent.