Low back pain (LBP) is a common condition. It is estimated that 84% of adults will present LBP symptoms at some point in their lives. Rarely, however, is LPB an indication of a serious medical condition, requiring further investigation. The treatment of non-specific LBP is based on non-pharmacological strategies, e.g., non-steroidal anti-inflammatory drugs (NSAID) or skeletal muscle relaxants. The use of epidural steroid injection (ESI) or facet joint injections relieves pain originating from degenerative spine disorders or a disk herniation, thereby providing rapid pain improvement, despite considerable long-term outcomes. Although rare, ESI complications can occur, and infections are infrequently described. This paper describes a rare case of an abscess in the psoas muscle, secondary to facet joint lumbar block. We report a male aged between 30 and 40 years old with LBP, who was submitted to a facet joint and ESI. The procedure evolved into a spinal infection of the psoas muscle. In addition, we present a brief literature review on psoas infections after spinal injection. Infection post facet joint lumbar block is very rare, with few publications in the literature. Early detection and the aggressive broad-spectrum antibiotic course must be initiated until adequate cultures are obtained and antibiotics prolong to at least four weeks.