Dried leaves and stems of Ilex paraguariensis St. Hil. (yerba mate) are used to make a popular beverage in some countries of South America, commonly known as “chimarrão”. The present study was designed to evaluate the occurrence of toxigenic Aspergillus in yerba mate in order to define the mycotoxin risk associated with this foodstuff. All samples tested were positive for fungal contamination, and the fungal load per sample ranged from 2.0 × 102 to 1.6 × 104 CFU/g. Aspergillus section Nigri was found in all samples and represented 76.5% of the total fungi isolated. Aspergillus section Circumdati, Aspergillus section Flavi and Aspergillus section Cremei were found at low frequencies. Thirteen different Aspergillus species were identified. The most common species found was A. luchuensis, which does not produce any harmful toxin for humans. A. niger, A. welwitschiae, A. flavus and A. novoparasiticus, all potentially toxigenic species, were found only in small quantities. The A. niger and A. welwitschiae strains were cultured to test for ochratoxin A and fumonisin B2 production. Only one strain producing ochratoxin A was found, but approximately 29% of the strains were positive for fumonisin B2. The A. flavus and A. novoparasiticus strains were tested for aflatoxins production, and 63% were positive. A. pallidofulvus, recently assigned to A. section Circumdati, was reported for the first time in herbs. All A. pallidofulvus strains analyzed in this study were negative for ochratoxin A production. In conclusion, A. section Nigri occurs with high frequency in yerba mate, and A. luchuensis is the predominant species. Although toxigenic species were found in this herb, the incidence was low.