Many currency analysts anticipate the yen weakening to around 105 to 110 per U.S. dollar by year-end, but as the final quarter of the year gets into full-swing the chance of the currency hitting those estimates later than forecast are rising.
Japan's currency firmed to a one-month peak against the greenback this week around 97, up more than 6 percent from the 4-1/2 year low set in May.
The rebound in the yen is a worrying sign for Japan's policy makers who have been hoping a weak currency would underpin the economic recovery, fuel business sentiment and a rally in Japanese stocks. This in turn is seen encouraging companies to spend or increase wages to help spur spending in the world's third biggest economy.
(Read more: Dollar shorts get louder as shutdown continues)
"Dollar/yen trade in recent weeks and months has been an exercise in frustration," Callum Henderson, global head of currency research at Standard Chartered Bank told CNBC.