The state security court sentenced Umar Sayil al-Khalayla, nephew of Jordanian-born al-Qaida operative Abu Musab al-Zarqawi, and two others to three years in prison.
"Because the defendants did not actually carry out the acts and because there were no explosives included in the trial, we sentenced them to three years," Judge Fawaz al-Baqur said.
"They had no contacts with Zarqawi, except for his relative since they are family members," he told Reuters.
Court documents said al-Khalayla was influenced by his uncle's conviction the Jordanian government was flouting Islamic strictures. The three men were arrested in May 2003.
Last month the state security court sentenced eight Islamist fighters to death, including al-Zarqawi who was tried in absentia, for killing a US diplomat in Amman.
Jordanian state television also showed last month what it
said were confessions by captured fighters saying they received orders from al-Zarqawi to attack targets that included the heavily guarded US embassy and intelligence headquarters in Amman.
A tape purporting to be the voice of al-Zarqawi said last month al-Qaida had planned to attack Jordanian intelligence. The US believes al-Zarqawi is in Iraq and organising attacks on US-led occupation forces and other targets.