Kaleme, which did not cite a source for its report, said the sentences were delivered last week giving the eight Facebook users a combined 123 years in jail.
They were charged with "insulting the supreme leader (Ayatollah Ali Khamenei) and the authorities, anti-regime activities, sacrilege and spreading lies," Kaleme said.
There was no official confirmation of the court ruling and AFP could not independently verify the report.
Access to the popular social networking site -- along with others which Iranian authorities regard as un-Islamic, immoral or undermining the Islamic establishment -- is obstructed by a massive filtering mechanism.
But tech-savvy Iranians have resorted to measures, known as anti-filters, to circumvent the restrictions.
According to Kaleme, an Iranian-born British woman is among the eight sentenced to prison.
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Roya Saberinejad Nobakht was reportedly arrested in Shiraz last autumn for comments she had made on her Facebook page, and was sentenced to 20 years in jail.
The report comes amid an ongoing clash between the hardliners and moderates, backed by President Hassan Rouhani, over Internet freedom in Iran.
Rouhani argues against fears that the Internet and its social media platforms pose a major risk to the Islamic republic's cultural and religious values, saying it must embrace the technology to progress.
Earlier this month, he vetoed a plan to ban WhatsApp, preventing implementation of curbs sought by a hardline committee in charge of web censorship.
But his push for social freedoms has angered conservatives who hold sway over several key institutions, including the judiciary.
Last week, the authorities arrested six young Iranians for dancing to US singer Pharrell Williams' hit "Happy" in a video that went viral.
The six were later released on bail.