The arrest of Mohamed Monir comes as Egypt steps up a press crackdown that it has been waging since Abdel Fattah el Sisi became president in 2014.
Egypt has arrested a veteran journalist who has been openly critical of the government after he appeared on the Qatar-based Al Jazeera network, the Committee to Protect Journalists said on Tuesday.
Mohamed Monir, 65, was arrested by plainclothes police officers in Giza early on Monday, the New York-based advocacy group said.
"Egyptian authorities must immediately and unconditionally release journalist Mohamed Monir and drop these baseless charges," it said.
Arrested for supporting Morsi?
"Monir is already in failing health, and to detain him pending trial during a pandemic is exceptionally cruel."
Monir has been remanded in police custody for 15 days on charges of joining a terrorist organisation, spreading false news and misusing social media.
His arrest comes as Egypt steps up a crackdown on the press that it has been waging since Abdel Fattah el Sisi became president in 2014, a year after he led the army's overthrow of his predecessor Mohamed Morsi.
The government regards Monir as a mouthpiece for Morsi's Muslim Brotherhood, now blacklisted as a terrorist organisation.
Police had previously raided Monir's apartment on Saturday.
He was not home at the time but he obtained footage of the raid from a camera in his building which he shared online.
In a defiant video message he posted on Facebook, Monir vowed that the authorities' attempt to arrest him would not stop him from speaking out.
In a family statement posted on Monir's Facebook page, his daughter Sara said, "He was merely exercising his freedom of speech and his words did not contain any incitement against the nation."
Links with Qatar in question
In May, the CPJ documented the arrests of at least four Egyptian journalists, including Sameh Haneen, a Coptic Christian who also faces charges of joining a terrorist organisation.
The Interior Ministry later published video footage of an alleged confession by Haneen, in which he claimed he had been paid thousands of dollars for producing videos critical of the government for Al Jazeera at the request of members of the Muslim Brotherhood.
Egypt and its Gulf allies — Bahrain, Saudi Arabia and the United Arab Emirates — have boycotted Qatar since June 2017, accusing it of supporting radicals and being too close to Iran, charges it denies.