Yahoo stock saw some unusual activity on Wednesday, with an investor betting that the initial public offering of Alibaba would send the shares higher, Jon Najarian told CNBC.

Yahoo, which owns 24 percent of Alibaba, could see boost in its shares "if it's a hot IPO," added Najarian, who is long calls.

The September 40 calls were purchased for 75 cents, along with the sale of 20,000 September 45 calls for 20 cents. "That represents 2 million shares of Yahoo. They did that for 55 cents," OptionsMonster's Najarian said following "Halftime Report."

But they could turn that into $10 million if they're right, if Yahoo trades to $45 or higher, he added.

The IPO of Chinese e-commerce site Alibaba is expected to take place in September.

— By CNBC's Bruno J. Navarro. Follow him on Twitter @Bruno_J_Navarro.

CORRECTION: This version corrected the potential gain to $10 million for $45 trades.