"Stock buyback, in my opinion, is a very good thing to do when your stock is cheap," he said at an investor conference hosted by Goldman Sachs Group Inc.
Dimon also said fourth-quarter trading revenue so far is "roughly equivalent" to last year.
The comments on buybacks come after JPMorgan shares have traded for a year at more than $100 and roughly two times tangible book value.
"The highest and best use of our capital is reinvesting it and we are starting to do that now," Dimon said, citing additional spending on technology, branches and loans to small business as examples.
"This notion that you should buy back stock at three times tangible book value as a return of capital to shareholders is crazy," he said.
He said he favors paying out dividends amounting to about 30 percent to 35 percent of annual earnings.
Protesters interrupted Dimon's comments twice to challenge JPMorgan over the financing of private prisons and immigration detention centers.
After the protesters were silenced, Dimon told the audience, "You should know that they do have legitimate issues."
He added, "Those prisons they are talking about are sanctioned by government agencies, audited by government agencies."
(Reporting by David Henry and Elizabeth Dilts in New York; Editing by Meredith Mazzilli)