Saeed Abedini, a naturalised US citizen and Christian convert, denied "charges of establishing churches to disrupt national security" in Iran and colluding to carry out crimes, his Iran-based lawyer Nasser Sarbazi was quoted as saying.
Abedini was not accused of espionage, Sarbazi said.
The 32-year-old was arrested in September on a return visit to Iran and alleged in a recent letter that he was beaten in prison, his wife Naghmeh and his US-based lawyer said last week.
Sarbazi said Abedini was to be temporarily released "in the next few days" after he posts a bail of four billion rials (nearly $115,000).
He will then be able to leave the country, Sarbazi added.
In the United States, Abedini's wife played down the accounts that her husband would soon be released on bail, saying the Iranian authorities had repeatedly promised to free him on bail but then failed to let him out when money was presented.
"This is a game to silence the international media," said Naghmeh Abedini.
"After the judge told Saeed's lawyer that bail was back on the table, the family in Tehran ran around in circles today (Monday) to make sure Saeed was let out on bail. But again the bail officer rejected bail."
She urged prosecutors to drop all charges against him, saying that "this is the only act that would allow Saeed to leave Iran and return to the US".
State Department spokeswoman Victoria Nuland said last week that the United States had "serious concerns" about the case and urged Iran to grant Abedini access to an attorney.
Iran's constitution following the 1979 Islamic revolution recognises the rights of several religious minorities including Christians, but the regime has targeted converted former Muslims.
Another Iranian Christian convert condemned to death, Youcef Nadarkhani, was released in September having spent two years in prison after his detention prompted international outcry.