The official SPA news agency on Saturday quoted Saudi Crown Prince Abd Allah bin Abd al-Aziz as saying that the suspect was arrested early in the morning.
"Today at dawn the security forces arrested a member of the deviant minority who admitted wanting to carry out an act in a neighbouring country," the prince said.
"He said he had come here to consult his brothers and was arrested at 5am (0200 GMT)," he added, without specifying which country the suspect targeted.
Saudi Arabia is fighting a fierce battle against a wave of violence, blamed on sympathisers of the al-Qaida network, that has claimed some 90 lives and wounded hundreds since May 2003.