The bug blocks browsers containing 128-bit encryption from accessing certain secure sites. Instead of content, the browser is greeted with a blank screen.
Microsoft (MSFT) officials said it's an inconvenience, not a security hole.
"We don't think it's a huge issue today, and we'll be posting a bug fix shortly," said Chris Carper, Microsoft product manager for the applications Internet and client group.
The fix will appear on Microsoft's Web site.
The bug affects sites using Secure Sockets Layers 2 and 3 to protect their transactions. Many financial institutions and companies asking for credit card information use those security levels.
The bug was first brought to Microsoft's attention by users who wrote to the Macfixit.com site to complain. According to the site, IE 4.0 for the Mac -- which was officially unveiled last week -- has set a record as the application receiving the most number of reported glitches in the first few days of its release.
In addition to the 128-bit problem, some users complained that the browser sometimes freezes or crashes. Microsoft officials said they would fix any further glitches in an upcoming release of the product.
The browser, brings many browser features to Apple users for the first time, including the ability to download and surf content while offline.