The employee is understood to be one of five people believed to be taken into custody by national security police on Monday in connection with the case linked to a pro-independence group known as Returning Valiant and an alleged terror plot.
The latest arrests come after nine people, including six secondary school students, were held last week over an alleged plot to blow up Hong Kong courts, cross-harbour tunnels and railways.
During that operation, officers said they found chemicals that could be turned into TATP, an explosive, and bomb-making equipment in a Tsim Sha Tsui hostel. Three of the students were charged and appeared in court last week.
On Monday, police escorted one of their latest detainees to the Emperor Group Centre in Wan Chai and carried out a search lasting around 45 minutes.
Emperor Group said it had suspended the worker. It also condemned illegal and violent acts, saying it will fully assist the police investigation.
Sources earlier told that RTHK that the five arrested on Monday are believed to be aged between 15 and 37, and three of them are students.