Mann said he was gratified that the university panel found he had not "seriously deviated from accepted practices within the academic community for proposing, conducting or reporting research or other scholarly activities," The New York Times reported.
A previous university inquiry cleared Mann of accusations of suppressing or falsifying data and destroying electronic records, the Times said.
The report issued Thursday concluded Mann had sometimes forwarded copies of unpublished manuscripts to colleagues without securing permission from their authors.
The investigation came in response to what has come to be called Climategate, which began when someone hacked into e-mails at a research center at the University of East Anglia in Britain. Skeptics argued some of the e-mails showed scientists misrepresenting data and other misconduct.
In an e-mail, Mann told the Times the controversy gives the appearance that "some would rather create distractions to fool the public, rather than confront the reality of human-caused climate change."
Mann, a former University of Virginia scientist, remains under investigation initiated in May by Virginia Attorney General Ken Cuccinelli.
Myron Ebell of the Competitive Enterprise Institute in Washington called Thursday's report from Penn State "a whitewash."