"Whenever you have these kinds of disruptive moves by central banks, there's always going to be fall out effects," said Boris Schlossberg, managing director of FX strategy at BK Asset Management.
Markets were caught off guard by the BoJ's announcement on Friday that it would expand purchases of exchange-traded funds (ETFs) and real estate investment trusts, extend the duration of its portfolio of Japanese government bonds (JGBs), and increase the pace of monetary base expansion.
The yen plunged nearly 3 percent against the U.S. dollar on Friday and extended its selloff on Monday, falling to a fresh-seven year low in early Asian trade. It last traded at 112.71.
Yen vs won
"The hottest currency war today is Japan vs Korea. That's probably the one to keep an eye on. The yen-won cross rate is very sensitive as Japan and Korea compete in a lot of key areas," said Sean Callow, senior currency strategist at Westpac.
The Japanese currency has fallen around 20 percent against the won since the BoJ launched its unprecedented stimulus program in April 2013.