The benchmark 10-year cash JGB yield and the 20-year yield slipped half a basis point each to 0.085 percent and 0.600 percent, respectively, their lowest since Aug. 22.

The 10-year JGB futures contract gained 0.06 point to 151.12, with a trading volume of 17,031 lots, by late afternoon trade.

In the super-long zone, the 30-year JGB yield fell 0.5 basis point to 0.815 percent, while the 40-year JGB yield was unchanged at 0.970 percent.

Japanese markets were closed on Friday for a national holiday.

On Friday, benchmark U.S. Treasury yields fell to eight-week lows and the yield curve flattened as falling stock and oil prices boosted safe-haven buying, while Germany's 10-year bond yield fell to its lowest since early September, pressured by weak euro zone PMI data.

In its buying operations on Monday, the Bank of Japan offered to purchase 450 billion yen of five- to 10-year JGBs and 180 billion yen of 10- to 25-year bonds, as well as 50 billion yen of 25-year or longer bonds, consistent with its previous purchase amounts for those zones.