"Yesterday, the first session of the trial was held and she was given an opportunity to speak in the court to present her defence," judiciary spokesman Ali Reza Jamshidi told reporters.
He said Saberi, who has been held in the notorious Evin prison in Tehran, is accused of "spying for foreigners… for America."
Saberi, a 31-year-old with dual Iranian-US nationality, risks the death penalty if convicted.
Iran's decision to put Saberi on trial comes despite calls by US Secretary of State Hillary Clinton for her release and US President Barack Obama's diplomatic overtures to Iran.
Jamshidi said the verdict was expected in one or two weeks.
He also dismissed remarks by US State Department spokesman Robert Wood who said last week that the charges against Saberi were "baseless."
"It is really funny that someone comments on a case without even seeing it," Jamshidi said.
Saberi was reportedly initially detained for buying alcohol, which is prohibited in the Islamic republic.
Last week Tehran's deputy prosecutor Hassan Haddad said Saberi was carrying out "spying activities under the guise of being a reporter."
"The evidence is mentioned in her case papers and she has accepted all the charges. She has been arrested under the laws of the Islamic Republic of Iran," he said.
In March, Iranian foreign ministry spokesman Hassan Ghashghavi said Saberi's press identity card was revoked in 2006 and that since then she had been working "illegally" in the country.
Haddad said Saberi had entered Iran as an Iranian citizen and Iran was unaware if she had any other citizenship.
"There is no evidence that she has another citizenship and the investigation is still on," he said.
US-born Saberi has reported for US-based National Public Radio (NPR), the BBC and Fox News, and had lived in Iran for six years.
Her parents, Reza and Akiko Saberi, have come to Tehran to pursue her case and have met her in the prison at least once.
Her father told NPR after seeing his daughter that Saberi wanted to see her lawyer to point out that some of the statements she made were "under pressure, under threat."
Last month the parents appealed to Iranian supreme leader Ayatollah Ali Khamenei for her release, saying she was in a "dangerous" mental state.
Iran, which does not recognise dual nationality and has had no ties with the United States for three decades, has detained several Iranian-Americans, including academics, in recent years.
Clinton delivered a letter to the Iranian delegation on the sidelines of an international conference on Afghanistan in The Hague on March 31, seeking Saberi's release and making appeals on behalf of two other US citizens.
Robert Levinson, a former FBI agent, vanished on the Gulf island of Kish two years ago, and student Esha Momeni has been prevented from leaving Iran despite being released from jail last year.
Momeni — a graduate student at California State University — was detained in Tehran on October 15 and released on bail in November, but has since been prevented from leaving the country.
She had travelled to Iran to carry out research on women's rights but was detained on national security charges.
Ghashghavi has denied receiving any letter from US officials asking about the three American citizens.
