The average two-year rate has this week reached 2.41%, a high last seen in September 2016, according to Moneyfacts data.
Rates have been steadily building over the past six months from a typical 2.17%, and since February alone have increased from 2.34%.
It comes as the Bank of England is expected to raise the base rate again in May, from its current levels of 0.5%.
Borrowers have been urged to act to secure a competitive deal sooner rather than later.
Charlotte Nelson from Moneyfacts said: “In recent weeks the trend of mortgage rates rising appears to be more than just a blip.
“As we move further into the year, borrowers will be expecting a move by the Bank of England.
“Therefore, if they haven’t done so already, they should consider a fixed rate deal so they can avoid inflated repayments.”