The Central Statistics Office said the number of people signing on, when adjusted for seasonal factors, was up 2,500 from July to 455,000.
A breakdown showed that women accounted for around 70% of the increase in August.
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July's surprise increase of 8,500 in the Live Register had been the biggest for a year.
The unemployment rate crept up from 13.7% in July to 13.8%.
The unadjusted figure for August rose by just 99 in the month to reach 466,923.
The CSO also said that there were just over 36,000 new claimants on the Live Register in August, a sharp drop from 60,000 the previous month.
Separate figures from the Department of Enterprise, Trade & Innovation show a fall in redundancies in August, though the figures remain high when compared with 2008.
4,399 lay-offs were notified to the department in August, a fall of almost 25% from the same month last year.
For the first eight months of the year, redundancies are down just over 20% from the same period last year to 43,449. This is still more, however, than the 40,000 recorded in the whole of 2008.
Commenting on the figures, Minister for Finance Brian Lenihan said it is clear that unemployment will peak in the next few months and will reduce thereafter.
He said there is complete unity of purpose in the Cabinet about the top priority in economic terms, and that that priority is jobs.
He said the Government has to put in position a credit system which can support an economic recovery.
Speaking on RTÉ's News At One, Minister for Social Protection Éamon Ó Cuív said the level of unemployment was 'a tremendous challenge'.
He said it was top of the agenda for the Government, but there would be a time lag until jobs followed from the projected pick-up in the economy.
He said the Government was rolling out many actions to help the unemployed, including back to education projects, the capital investment plan, investment in research and innovation, employers' PRSI exemption, the employment subsidy scheme, and other schemes.
Fine Gael's Richard Bruton said priority should be given to restoring credit facilities to stop businesses closing.
