Teodorin Obiang Nguema, the son of the country's president, is accused of money laundering. He has not commented.
Swiss authorities have seized 11 cars in total.
Among them was reportedly a Porsche valued at more than $830,000 (£667,000) and a Bugatti Veyron which sells for $2m (£1.7m).
The accused is due in court next year in France on similar charges, which he denies.
Prosecutors in Geneva say he has plundered his country's oil wealth to buy luxuries, including a private jet and Michael Jackson memorabilia.
Equatorial Guinea, a small country on the west coast of Africa, struck oil in 1995.
Its president, Teodoro Obiang Nguema, is Africa's longest serving leader. He has been described by rights organisations as one of Africa's most repressive leaders.
He seized power in 1979.
MrObiang, 47, was promoted in June by his father to be vice-president.
He was already set to face trial in France next year on corruption and embezzlement charges.
He is challenging those charges at a UN court and is not expected to appear before the French judges.