Home sales rose 1.7 percent from July to a seasonally adjusted annual rate of 5.48 million sales per year.
July's figure on existing home sales was revised slightly higher to 5.39 million.
Sales for the month are also 13.2 percent higher than August 2012, when the annual rate stood at 4.84 million.
The NAR also said the median price of home in August rose by double-digit figures compared to a year earlier for the ninth consecutive month.
The median prices rose 14.7 percent from August 2012 to a national median price of $212,100. August made it 18 consecutive months with prices rising from the same month a year earlier.
Despite the gains, NAR Chief Economist Lawrence Yun warned that "several market frictions" could create uneven sales in the next few months.
"Tight inventory is limiting choices in many areas, higher mortgage interest rates mean affordability isn't as favorable as it was, and restrictive mortgage lending standards are keeping some otherwise qualified buyers from completing a purchase," Yun said in a statement.
Yun said that rising interest rates had pushed sales, as customers looked to lock in deals before rates got any higher.
The trade group said there were 2.25 million existing homes on the market at the end of August, a 0.4 percent increase from the end of July.
The number of homes for sale represents a 4.9-month supply at the current sales pace, a figure that is down from the 5-month supply in July, NAR said.
Unsold inventory is 6.3 percent below August 2012.
"Limited inventory in some areas means multiple bidding remains a factor," Yun said pointing out that 1.7 percent of homes sold closed at prices above the original asking price.
Sixty-three percent, however, sold below the list price, he said.