According to police, the controlled explosion showed no trace of a suspect device. Prince Charles was delayed but still attended the reception.
An area around the central London property opposite St James's Palace was sealed off at 1330 (GMT), a Scotland Yard spokesman said.
Suspicions had been aroused after the vehicle's registration number did not show up on a search of the police computer.
The controlled explosion was carried out 30 minutes later.
The Prince of Wales had been due to attend a reception for the African Medical and Research Foundation (AMREF) between 1300 and 1400.
However, according to a spokeswoman for the Prince, he delayed his arrival after his office was alerted shortly before 1300 .
He finally arrived at the reception around 1415.
A Scotland Yard spokesman said: "There was a controlled explosion carried out by the anti-terrorist branch on a motor scooter at 1400.
"There was no trace of any device or explosives so it was innocent and things are returning to normal."
The Prince of Wales's spokeswoman said: "As patron of the Foundation he was due to attend the reception to mark the 1998 African Health Conference.
"He was due to arrive there between 1300 and 1400 but...the area was sealed off.
"In order not to disappoint guests he went for the latter part of the reception."
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(27 Mar 98 | UK)
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