Arkansas coach Eric Musselman made the announcement in a media session on Monday.
By choosing not to hire an agent, Joe could return to school next season.
Joe, a 6-foot-5 sophomore, averaged 16.9 points and 4.1 rebounds per game this past season and led the SEC in 3-point field goals. He missed five games after having surgery on his right knee, and the Razorbacks lost all of them. He scored 21 points in his return, a win over Missouri.
As a freshman, Joe averaged 13.9 points and 2.8 rebounds.
He is the 61st-ranked prospect in ESPN's draft prospect rankings.
Last month, Arkansas guard Mason Jones declared for the draft. The Associated Press' co-SEC player of the year averaged 22.0 points, 5.5 rebounds and 3.4 assists this past season.
The Associated Press contributed to this report.