However, the number of sales, which were trending upwards in the past few months, was still down over the year, with only 420 sales (32.2 per cent less) compared to the 1306 sold last May.
The agency's managing director, Peter Thompson, said although the number of residential properties sold in May was low compared to previous years prices were still strong.
However, he said sale stock was increasing.
"With a sound number of new listings, total listings at their highest for the past five years and low sales, there was greater pressure on prices to fall than has been experienced for some years."
In May, the agency had 1734 new listings, up 441 (34.1 per cent) from the previous month and had available stock of 4298, up 84 (2 per cent) across the same time period.
But Thompson said prices were likely to remain flat until after the election.
"The vendors who are achieving a sale are those who accept that prices are flat, and are likely to remain that way until the September election is behind us."
ASB senior economist Jane Turner said turnover had been steadily declining over the past two years "as tighter loan-to-value lending limits, particularly those targeted at investors, have seen the Auckland market cool from extremely overheated levels".
While Turner said the number of houses available for sale had risen to a level not seen before 2012, "nonetheless, the number of houses available for sale relative to demand remains below the historical average and consistent with a still-tight housing market, albeit more balanced compared to recent history".
She echoed Thompson's sentiments that prices in the Super City were likely to remain subdued.
"However, sluggish growth in housing construction relative to population growth, should keep a floor under prices."