The five day extension means that detectives can now hold the three until Tuesday June 16.
Detectives from the West Midlands Counter Terrorism Unit (CTU) appeared before London's Westminster Magistrates Court via video link earlier today to submit their request for a warrant of further detention.
The three were arrested at 6am yesterday June at their home addresses. The two men are aged 21 and 27, and the woman is aged 21.
Police said they were keen to stress that while the arrests were pre-planned and intelligence led, there was no imminent threat to public safety.
Searches at addresses in Walsall are continuing and a number of items have been removed for forensic examination.
These pictures show searches carried out at homes in Walsall after the arrests.
Searches at eight addresses in Walsall, and one in the Moseley area of Birmingham have been carried out.
The three are being held at a station in the West Midlands Police area.
The arrests were made under terrorism legislation, meaning officers had an initial 48 hours to question the suspects before charging, releasing or applying for a warrant of further detention.
Anyone with information about possible terrorist activity should call the police Anti-Terrorist Hotline: 0800 789 321 or dial 999 in an emergency.