The report by Globo's TV news programme Fantastico was based on documents Guardian journalist Glenn Greenwald obtained from former NSA contractor Edward Snowden.
The programme showed what it said was an NSA slide dated June 2012 displaying passages of written messages sent by Mexican President Enrique Pena Nieto, who was still a candidate at that time. In the messages, Mr Pena Nieto discussed who he was considering naming as his ministers once elected.
A separate slide displayed communication patterns between Brazilian President Dilma Rousseff and her top advisers. Both slides were part of an NSA case study showing how data could be "intelligently" filtered by the agency's secret internet surveillance programmes disclosed in documents leaked by Mr Snowden in June, Fantastico said.
Brazil's government, already smarting from earlier reports that the NSA spied on the emails and phone calls of Brazilians, called in US Ambassador Thomas Shannon to explain the new allegations that the agency had spied on Mrs Rousseff herself.