Khan, his sons, aged seven and five and their maid all escaped unhurt after they handed over cash, credit cards and his mobile phone, spokesman Akbar S. Babar said.
Babar said the ambush appeared well planned as a vehicle pulled in front of Khan's vehicle and forced him to stop on the side of the road about 6:00 pm (1300 GMT).
When Khan, who was driving, stopped the vehicle, two men brandishing semi-automatic weapons appeared from some bushes and demanded they hand over their valuables.
"This shows an overall breakdown of law and order in Pakistan," Babar said.
"Imran Khan feels that VIPs and ordinary people have no protection at all."
As well as being a cricketing hero in Pakistan, Khan, 51, is a member of parliament and a fierce critic of President Pervez Musharraf, who came to power in a bloodless coup in 1999.
Khan comes from a prominent family of ethnic Pashtuns and is an Oxford University graduate in politics, philosophy and economics.
He rose to fame playing 82 Tests for Pakistan, 48 of them as captain, and skippered the team to one-day World Cup glory in Australia in 1992.
His nine-year marriage to British socialite Jemima Goldsmith, which ended in June, also kept him regularly in the headlines.