The alleged coup was planned to take place on Thursday, the army said
Guinea Bissau says it has foiled an attempt by the head of the country's navy to overthrow President Joao Bernardo Vieira.
An army spokesman said Rear Admiral Americo Bubo Na Tchuto was arrested after telephoning senior officers to ask for help in ousting Mr Vieira.
The alleged coup comes amid political turmoil in Guinea Bissau.
The president has dissolved parliament, a month after one of the three main parties quit the unity government.
"We have foiled a coup attempt that should have been carried out early on Thursday by a group of officers led by Rear Admiral Jose Americo Bubo Na Tchuto, head of the navy," an army spokesman told reporters in the capital, Bissau.
Col Arsenio Balde said that Mr Na Tchuto had asked several top officers to assist in his plan to depose the president including the army chief of staff, who ordered his arrest.
He said that Mr Na Tchuto would remain under house arrest while an investigation continued.
Guinea Bissau, one of the world's poorest countries, is not unused to coups.
President Vieira first came to power on the back of a military coup in 1980, while he was head of the armed forces.
He was toppled in 1999 but returned to win the presidency as an independent in 2005.