House prices rose 0.6% year-on-year after a 0.3% rise in July, Nationwide said. On the month, prices were flat.
British house price growth has sagged since the 2016 Brexit referendum - especially in London and neighbouring areas - but at a national level the market appears to have stabilised, surveys suggest.
"With the economy struggling and the outlook currently highly uncertain, we suspect that house prices will remain soft despite the recent pick-up in housing market activity - which could well prove temporary," said Howard Archer, chief economist adviser to the EY ITEM Club consultancy.
He added that he expected house price growth of just 1.0% for 2019 as a whole, using Nationwide's measure.
On Tuesday, industry body UK Finance said British banks last month approved the most mortgages since February 2017. Official figures from the Bank of England are due at 0830 GMT.