The 25-year-old man, a dual UK-Iranian national, was arrested on suspicion of preparation of terrorist acts under the UK's Terrorism Act.
He was arrested on Thursday in London, where searches of two properties have now ended.
The investigation into the incident was ongoing, England's Counter Terrorism Policing (CTP) said.
It comes after five British nationals, all in their mid-20s, were arrested on suspicion of explosives offences and terrorism and then bailed.
Three suspicious vans were spotted near the military site in Gloucestershire last weekend.
Scores of residents were evacuated from their homes near the base as armed police officers and army bomb-disposal experts swooped on the rural area.
Senior CTP national co-ordinator Vicki Evans previously said the investigation is "hugely complex", adding specialist teams are "interrogating multiple lines of inquiry".
"As we've made clear, we're looking at all possible angles – including possible foreign state involvement," she said.
Prime Minister Andy Burnham has said there were "strong indications" Iran played a part in the incident near the Gloucestershire military base.
RAF Fairford has been used in recent months by US bombers after former prime minister Sir Keir Starmer granted the US permission to use British bases for "defensive" strikes against Tehran during the Middle East war.
Counter-terror police have said a quantity of petrol but no explosive devices were found in the vans that sparked the security alert near the airbase.
On Thursday, Israeli Prime Minister Benjamin Netanyahu claimed Israel handed Britain intelligence about the suspected terror plot.
Netanyahu said his country warned UK authorities about the "Iranian-sponsored attack" shortly before Britain's announcement of a ban on trade with illegal Israeli settlements in the West Bank.
Top US officials have criticised the decision to grant the suspects bail, with President Donald Trump saying "I wouldn't have done that" and Secretary of State Marco Rubio saying a lot of people were "disturbed" by the move.
- with AP
10°C