Police arrested nine people last week and five more on Monday.
Three of those arrested last week, all of them teenage secondary school students, were charged and appeared in court earlier.
The police said on Tuesday they have charged three more people – a 15-year-old who was arrested on Monday, along with an 18-year-old woman and a 24-year-old man held last week – and accused them of violating the national security law.
They will appear in West Kowloon Court on Wednesday morning.
Officers said the other four arrested on Monday have been released on bail and will report to the force in a month’s time.
During last week’s arrests, the police spoke of an alleged plot to make bombs and plant them at public facilities such as courtrooms, cross harbour tunnels and railways.