The students, in their 20s and from the U.S. state of Virginia, were detained in December in the central Pakistani town of Sargodha, 190 km (120 miles) southeast of the capital.
They have not been formally charged but could face lengthy prison terms if found guilty.
The case of the Americans, who were arrested days after arriving in Pakistan, has raised alarm over the danger posed by militants using the Internet to evade tighter international security measures and plan attacks.
A defense lawyer for the five men, Hassan Katchela, told Reuters by telephone that an anti-terrorist judge in Sargodha turned down the plea for their release on bail.
"We were not expecting the dismissal, as despite our repeated demands for evidence and charges, the prosecutors failed to provide anything substantial against them," he said. "Now we will approach a higher court."
A panel of defense lawyers for the men said the charges brought against their clients were "vague" and requested an anti-terrorist court on Tuesday to order their release on bail.
Police have said emails showed they contacted Pakistani militants who had planned to use them for attacks in Pakistan, a front-line state in the U.S.-led war against militancy.
The men -- two of them of Pakistani origin, one of Egyptian, one of Yemeni and one of Eritrean origin -- told the court earlier they only wanted to provide fellow Muslims in Afghanistan with medical and financial help.
They have accused the U.S. Federal Bureau of Investigation and Pakistani police of torturing them and trying to frame them. Pakistani authorities have denied the accusations of mistreatment.
