Government spokesman Nasser Judeh accused the activists of plotting against public institutions and officials, but did not elaborate on any specific attack plans.
He spoke as a Palestinian security delegation led by Major-General Tareq Abu Rajab, the head of Palestinian General Intelligence, began a two-day visit to Jordan to investigate the evidence against the Hamas activists.
The senior Palestinian diplomat in Jordan, Atta Khairy, said Abu Rajab was briefed on the facts and "shown evidence on the arms smuggling allegedly by Hamas activists."
Hamas officials, along with the Syrian government - which hosts Hamas' exiled leadership - have denied the allegations since the cache's discovery three weeks ago.
Judeh said the arrests took place in late April when police seized the weapons, including missiles and rockets, that Hamas members had stockpiled in various parts of the country. He said the seized arms included Iranian-made Katyusha rockets and light anti-tank weapons known as LAW missiles.
'Hamas seeking to send activists to Syria for training'
He said the government suspected that more arms had been hidden but "Not yet discovered."
Judeh said Hamas had been seeking to "recruit elements to operate" in the kingdom as well as bring in activists from the Palestinian territories "to send them to Syria and Iran for training on intelligence, security and military activities."
Abu Rajab came to Jordan on behalf of Palestinian President Mahmoud Abbas, not his Hamas-led government, which turned down a Jordanian request to send a delegation.
His five-member team, including his deputy Tawfik Tirawi, held talks behind closed doors with top Jordanian security officers at the Amman headquarters of the General Intelligence Department, said Khairy, head of the Palestinian mission in Jordan.
A Jordanian security official with close knowledge of the talks said the Palestinians were briefed on the "activities, plans and surveillance carried out by Hamas elements with the intent of threatening Jordan's national security." He spoke on condition of anonymity because of the sensitivity of his position.
Hamas activists' confessions would air on state television late Thursday, to address the Jordanian public's suspicions about the accusations, Judeh said.
The Islamic Action Front, Jordan's largest Muslim opposition group, has accused the government of exaggerating the arms discovery and bowing to US pressure to undermine the Palestinian government.
Other opposition groups said the arms cache may have been destined for the West Bank, but was being stockpiled in the kingdom awaiting safe passage across the border with Israel.
Gradually disclosing information about the plot, the government said two weeks ago that the Hamas activists were in the final phase of planning an attack on unspecified targets in the kingdom under orders from a Hamas official in Syria.