Michael McCord said many people bought larger homes during the Covid pandemic, influenced by low interest rates.
He said those with short-term, fixed-rate mortgages would soon face higher repayments when their deals expire.
There was a significant rise in house sales in Northern Ireland between the end of 2020 and the middle of 2021.
However, interest rates have risen in recent months and this week the Bank of England warned it may hike interest rates even higher in an attempt to curb inflation.
Many mortgage lenders are already raising interest rates or have withdrawn products before putting them back on the market at higher rates.
Speaking on the BBC's Good Morning Ulster programme, Mr McCord said that would lead to a significant increase in repayments for homeowners who are due to move to a new mortgage deal.
"We have consumers coming to the end of their terms and a core issue is that they actually might not qualify or pass the affordability checks with their current lender for their current property on their existing loan, which would be perilous," he explained.
Mr McCord warned that some first-time buyers could be "locked out of the market and locked into the private rental sector" because of the rising upfront costs of getting a mortgage.
He also suggested there was "bit of a perfect storm" that could lead to significant falls in property prices.
But he said that there may be some protection from that in Northern Ireland due to the limited supply of homes for sale.