When the South African leader arrived in the US, his party - the African National Congress - was still designated as a terrorist organisation by the US government, The Independent reported, adding that the agency already had tabs on Mandela's movements from an informant close to his entourage.
The partially redacted files, obtained by Ryan Shapiro from the Massachusetts Institute of Technology and shared with Al Jazeera, contain 334 pages of FBI records from June 1990.
Shapiro is involved in an ongoing legal battle with the National Security Agency, CIA and Defence Intelligence Agency for records on Mandela.
"Not only did the FBI heavily redact and withhold documents, but there's virtually no discussion of US intelligence community involvement prior to Mandela's 1990 release from prison," Shapiro said.
Mandela received a rapturous welcome on his tour of eight US cities.
He had just been released from prison after 27 years and had become an international icon for his struggle against apartheid.
One of the challenges for security services during the visit was keeping Mandela safe in the wake of numerous death threats.
The FBI logged threats from white supremacists, a neo-Nazi group, the Ku Klux Klan, the Aryan Knights of the Great Forest and other groups.
Mandela was elected as South Africa's first black president in 1994. He died aged 95 at his home in Johannesburg in December 2013.