According to the organisation, the restricted lending market is making it difficult for many potential buyers to find the required finance for their purchase.
In addition, the number of new properties coming on to the market in the US has also fallen, which has "limited buying opportunities", according to NAR chief economist Lawrence Yun.
The result of this constrained mortgage market coupled with a reduction in inventory is pushing house prices higher, he explained.
Mr Yun added the average value of US real estate has been bolstered by a decline in the number of distressed properties being offloaded.
Last month, the Standard & Poor's/Case-Shiller home price index for the US found average residential real estate values increased by 1.3 per cent in April, compared to the previous month. However, the report pointed out that prices were still down on an annual basis.