Japan still lacks a culture of shareholder and draws more investors to meet competition from Asian bourses, Mr McCreevy said.
"I am loath to say what Japan should do because the culture here has been very, very against any type of (shareholder) activism," Mr McCreevy said.
"But as Japan opens up its markets over time ... I think there is an inevitability that some type of semi-European or semi-US kind of philosophy will take place here as well."
Mr McCreevy is visiting Japan to meet government officials, including Financial Services Minister Yuji Yamamoto, to build on financial regulatory ties and exchange views on financial services reform. He is scheduled to visit the Tokyo Stock Exchange, Asia's largest bourse, tomorrow.
Japanese firms have traditionally been averse to mergers and acquisitions but have seen a growing wave of shareholder activism, with funds such as Steel Partners and Dalton Investments building up stakes in what some see as undervalued companies and pushing management to change.
After an internal tussle, Japanese digital camera and optical lens maker Pentax Corporation accepted a tender offer last month from high-tech glass maker Hoya Corporation, largely due to mounting pressure from its shareholder Sparx Asset Management, a Tokyo-based investment fund, to do so.
Mr McCreevy, the commissioner in charge of the EU's internal market and services, said the question of shareholder activism has been a contentious issue even within the 27-nation bloc, with member countries having differences in views.
How Japan deals with the growing presence of shareholder activism is entirely up to its authorities, Mr McCreevy said. "But if it does (open up markets more), my main job as European commissioner is to ensure that European companies are not discriminated against" when operating in Japan, he said.
Japan, the world's second-biggest economy, lags far behind rivals in global equity trading volume, accounting for a mere 9 per cent, hurt by high taxes and opaque regulations.