Earlier in the day, Icahn revealed on Twitter that he had taken a "large position" in Apple, adding, "We believe the company to be extremely undervalued."
Icahn's stake was reportedly worth more than $1 billion, according to Dow Jones.
(Read more: When to expect Apple iPhones, iPads, iWatch and iTV )
Brian Kelly of Brian Kelly Capital said that it would be tough for Icahn to effect large-scale action.
"I think it's going to be a very difficult road here," he said. "Maybe the end up doing a little bit more of a buyback, but I wouldn't expect major changes at Apple just because Carl's in here. It's a massive, massive company."
(Read more: Apple sets iPhone launch date, Wall Street says buy now )
Tim Seymour of EmergingMoney.com noted that Icahn "didn't necessarily say how aggressive" he would be.
"He basically said he thinks the company's very undervalued," Seymour added.
Dan Nathan of RiskReversal.com said that there was a choice for any potentially new Apple investor.
"It's made this amazing comeback from below $400 to almost $500. It's probably going to touch there in the next day or so," he said. "So, at this point, if you want to jump in and ride Icahn's coattails, you have to make a decision here whether this is essentially a product-innovation story at some point in the future, or if it's a financial engineering/value story."
Nathan added that "this was much of the debate for the last year when this stock wallowed."
— By CNBC's Bruno J. Navarro. Follow him on Twitter
Trader disclosure: On Aug. 13, 2013, the following stocks and commodities mentioned or intended to be mentioned on CNBC's "Fast Money" were owned by the "Fast Money" traders: Tim Seymour is long BAC; Tim Seymour is long SBUX; Dan Nathan is long FB; Dan Nathan is long JCP; Dan Nathan is short BBRY; Dan Nathan is long VIX; Dan Nathan is short IWM; Karen Finerman is long AAPL; Karen Finerman is long BAC; Karen Finerman is long C; Karen Finerman is long JPM; Karen Finerman is long TGT; Karen Finerman is long GOOG; Karen Finerman is long M; Karen Finerman is long CAT; Karen Finerman is long JCP; Karen Finerman is long SPY; Karen Finerman is long MDY PUTS; Brian Kelly is short Aussie dollar; Brian Kelly is long US dollar; Brian Marshall is long AAPL.