In a tweet, he told investors to expect an "in-depth report" in two weeks.
Apple shares were volatile Tuesday after the company posted quarterly earnings and revenue that topped Wall Street's expectations on Monday.
The stock has jumped 19 percent this year.
Icahn has long urged Apple to increase its capital return program, which the tech giant announced it would boost on Monday. Apple said it would expand its program to $200 billion from $130 billion previously.
Shares traded around $132 on Tuesday, a price-to-earnings ratio of about 16. Apple's market cap at the price sat at roughly $765 billion.
In February, Icahn said the stock should trade at $216 per share, which would value Apple at $1.3 trillion.