The BOJ on Monday bought a total of 1.23 trillion yen ($11.95 billion) of one- to 10-year JGBs as a part of its bond purchasing scheme.
The benchmark 10-year JGB yield was up half a basis point at minus 0.055 percent, while the 30-year yield rose 1.5 basis points to 0.510 percent.
The steepening of the JGB yield curve was in line with developments in the Treasury market.
The 10-year/30-year Treasury yield spread is the steepest in about a month, as the 30-year bond underperformed on Friday with its yield rising sharply after Federal Reserve Chair Janet Yellen suggested the central bank may allow inflation to exceed its 2 percent target.