West Midlands Police said the man had been detained in Reading and the woman in Wokingham by counter-terrorism officers at about 19:30 BST.
The pair, believed to be friends, were taken to a police station in the West Midlands for questioning.
The force said the arrests had been intelligence-led.
The suspects did not pose any imminent threat, a spokesperson added.
Supt Robin Rickard from Thames Valley Police said the arrests "were part of an ongoing investigation by West Midlands Counter Terrorism Unit and were pre-planned".
"Officers from Reading and Wokingham are providing support and there are searches taking place at the suspects' home addresses," he said.
A 24-year-old man and a 23-year-old woman have been arrested in Berkshire on suspicion of preparing for acts of terrorism in the UK.