Consumer confidence had a surprising dip in September, according to data released today.

The Westpac-Melbourne Institute consumer sentiment index fell to 113.2 in September from 119.2 the previous month, erasing a 5.4 per cent gain in August in the process.

The survey of 1,200 people now stands 5.1 per cent lower than a year ago. Still, a reading above 100 points showed there were more optimists about the economy than pessimists.

Westpac chief economist Bill Evans said the result came as a mild surprise, given the steady cash rate in August, a drop in unemployment figures to 5.1 per cent, and two-week rally in equity markets and the Australian currency.

He had expected positive news throughout the month to trigger a further increase in sentiment. All components of the consumer sentiment index, however, fell in September.

Mr Evans said the August reading may have overstated confidence and that the September level of the index is probably a more reasonable indication of the level of consumer confidence.

The index measuring expected economic conditions over the next 12 months declined by 7.2 per cent and expected conditions over the next 5 years slumped by 6.1 per cent.