British Gas is keeping its current gas and electricity prices on hold until August.
The company said it was able to hold tariffs in the face of higher wholesale prices by cutting its costs.
However, Scottish Power has said it is raising its dual fuel prices by an average of 7.8% from 31 March. It blamed smart meters and low carbon energy costs for the rise.
Energy regulator Ofgem urged customers to shop around for a better deal.
Scottish Power's move makes it the third of the UK's big six energy suppliers to announce price rises.
- Scottish Power's standard electricity prices will increase by an average of 10.8% and gas prices by 4.7%. About one third of its customers - 1.1 million people - will be affected by the change
- Npower is raising its standard tariff electricity prices by 15% from 16 March, and gas prices by 4.8%
- EDF Energy cut its gas prices by 5.2% in January, but its electricity prices are due to rise by 8.4% on 1 March
Sluggish switchers: Kevin Peachey, personal finance reporter
This decision will be a relief to five million British Gas customers - but that may only be temporary.
With rumours swirling of a British Gas price rise, the company has now effectively said no increase will occur for four spring and summer months.
Yet with other suppliers changing their tariffs, there will be a chorus among government, the regulator and others urging householders to switch.
Is the message getting through after years of repetition? A recent report by the competition authorities found that a third of the 7,000 people it asked did not realise that switching was an option.
Announcing the price increases, Colin McNeill, UK retail director for Scottish Power said: "This price change follows months of cost increases that have already led to significant rises in fixed price products that now unfortunately have to be reflected in standard prices."
However, British Gas owner Centrica said its price freeze had been made possible "despite increases in external costs".
"We are engaging all of our customers on our standard tariff with a range of new offers. It is important to us to ensure that customers continue to make an active, informed choice over their energy."
In a statement, energy regulator Ofgem said: "We would urge consumers to take advantage of the deals available from the many different suppliers and to shop around for a better deal if their supplier puts up their prices.
"This will put pressure on all suppliers to ensure they run their businesses efficiently to keep any impact on bills as low as possible."
When Npower announced its price rises, energy regulator Ofgem told it to "justify" to its customers why it was introducing one of the largest increases for years.
Energy price rises are likely to fuel inflation concerns.
Rising air fares and food prices helped to push up UK inflation to 1.6% in December, its highest rate since July 2014.