Jordanian state television quoted a security official on Wednesday as saying that intelligence services foiled an attack on "a vital civilian installation" and arrested a Libyan and two Iraqis.
The Jordanian authorities are also trying to track down a Saudi national and three Iraqis who took part in the plot and who apparently fled to a neighbouring country.
"The intelligence services seized four kilograms (8.8 pounds) of heavy explosives," the security official was quoted as saying.
Apparently the explosives were the same as those used in three hotel bombings in Amman on 9 November that killed 60 people and which were claimed by the al-Qaida branch in Iraq headed by Jordanian fugitive Abu Musab al-Zarqawi.
Stay away warning
Television showed pictures of the three men who were arrested in connection with the plot and identified them as Libyan national Mohammed Saeed al-Dorsi, 25, and Iraqi nationals Mohsen al-Lussi, 34, and Abdel Karim Jumeili, 48.
All three suspects have been referred to the state security court, a military tribunal that deals with conspiracy plots and terrorist-linked cases.
The suspects still at large were identified as Saudi national Turki Abdullah and three Iraqis: Saad al-Obeidi, Saad al-Nuaimi and Yussef al-Obaidi.
Meanwhile the Israeli government's anti-terrorism office has recommended that its citizens stay away from Arab countries because of a heightened fear of "terrorist" attacks.
Jordan is one of only two Arab countries to have a peace deal with Israel.