The four were taken from their homes in different parts of the northern city late Friday, the Journalistic Freedoms Observatory (JFO), an Iraqi organisation, said in a statement.
Mosul activists and a former security official confirmed to AFP that four Mosul University students had been detained and taken to an unknown location.
A journalist who was arrested for similar reasons in June, Jala al-Abadi, was executed in mid-July.
According to JFO, IS holds at least eight journalists from the province of Nineveh, of which Mosul is the capital.