Officers said they received an anonymous complaint about the post in March last year, with the complainant expressing concern and fear.
The post in question described a sweep Ho said he was planning to conduct against illegal gambling in a Tin Shui Wai public housing estate.
The post was accompanied with a photo of a knife, the police said.
Officers arrested Ho on Wednesday morning and seized two computers and a knife.
They said Ho was due to appear before Tuen Mun Magistracy on July 22.
Asked why the arrest was made over a year after the alleged incident, the police said the investigation had been complicated and they had twice consulted the Department of Justice.