An internal investigation at Apple Computer ( AAPL) found irregularities related to certain stock-option grants made between 1997 and 2001.

Following the announcement, shares of Apple slipped $1.47, or 2.5%, to $57.50 in after-hours trading on Instinet.

The company said late Thursday that one of the grants in question was to CEO Steve Jobs, but "it was subsequently cancelled and resulted in no financial gain to the CEO."

However, Jobs was awarded restricted shares following the cancellation of that grant.

A special committee of Apple's outside directors has hired independent counsel to perform an investigation and the company has informed the Securities and Exchange Commission.

Apple executives will refrain from commenting further on this matter until the independent investigation is concluded.

"Apple is a quality company, and we are proactively and transparently disclosing what we have discovered to the SEC," said Apple CEO Steve Jobs. "We are focused on resolving these issues as quickly as possible."