Police did not disclose specific details of the allegations. They said he was arrested in relation to a case involving another senior editor, who had been arrested in June for allegedly endangering national security through his articles.
Police said on Wednesday that they arrested a 51-year-old former executive editor-in-chief on suspicion of endangering national security by colluding with foreign forces.
Apple Daily was closed down on June 24 after its assets were frozen.
Eight people related to Apple Daily have been arrested so far.
But police have been continuing to detain former senior members of the newspaper. On June 27, they arrested another senior member at a Hong Kong airport while he was attempting to leave for Britain.