The platinum-selling artist, whose real name is Joseph Cartagena, was once a Billboard chart topper with hits like the duet "What's Luv" with the R&B singer Ashanti.
Cartagena entered the plea in federal court in Newark because some of the companies he earned money from are incorporated in New Jersey.
The 42-year-old Miami Beach, Fla., resident entered pleas to two counts covering years 2007 and 2008. His sentencing will take into consideration the government's initial allegation that he failed to pay income taxes for years 2007 through 2010. Federal prosecutors said the total tax loss to the government for those four years was $718,038.
Wearing a navy suit, Cartagena looked fit and considerably slimmer than the former size that had earned him his rapper nickname.