The yield on Japan's 10-year government bond has risen to its highest level since January 2014.
It hit 0.7 percent at one stage on Monday.
A move by the Bank of Japan in July to slightly relax its grip on long-term yields has been putting upward pressure on the benchmark bond's yield.
BOJ Governor Ueda Kazuo has since indicated the possibility of another tweak in the near future. He has told the media that "all the materials" for a decision on monetary policy are likely to be gathered by the end of this year.
He said the lifting of the BOJ's negative-interest rate policy is one choice.
Fixed-interest rates on mortgages usually reflect the benchmark bond's rates.
Japan's leading banks have raised their fixed rates to apply in September in the wake of rising long-term interest rates.