Fifteen species of Agistemus Summers were previously reported from Brazil. Herein, Agistemus bahiensis sp. nov. is described and illustrated from specimens collected on Annona muricata L. (Annonaceae), Euterpe oleracea Mart. and Polyandrococos caudescens (Mart.) Barb. Rodr. (Arecaceae) at the Southern Coastal Region of the state of Bahia, Brazil, between April 2007 and August 2017. The new species mainly differs from all other similar species by having a pattern of longitudinal striae as a band of dashes on the hysterosomal shield. It can also be distinguished by the dorsal setae measurements and the distances between them, being all dorsal setae of equal size in the new species (22–29), except for ve, which exceeds 30 (29–35), with none of them reaching the bases of the subsequent setae. Dorsal setae are always greater than 30 and ve is always greater than 55 (56–80) in the other five similar species. A key to Brazilian species of the genus is provided.