A statement from City of London Police said:
The Old Bailey has been evacuated following the discovery of a suspect package.
City of London police officers are at the court. One man has been detained while further checks are carried out.
Significant road closures are in place around the court.
The spokeswoman would not comment on reports the suspect package was found in Court 11, where Pavlo Lapshyn in being sentenced for bombing three mosques, and murdering a Muslim pensioner in a series of racist attacks.