A novel Gram-positive bacterium, designated $SYB2^T$, was isolated from wastewater reservoir sediment, and a polyphasic taxonomic study was conducted based on its morphological, physiological, and biochemical features, as well as the analysis of its 16S rRNA gene sequence. During the phylogenetic analysis of the strain $SYB2^T$, results of a 16S rRNA gene sequence analysis placed this bacterium in the genus Arthrobacter within the family Micrococcaceae. $SYB2^T$ and Arthrobacter protophormiae ATCC $19271^T$, the most closely related species, both exhibited a 16S rRNA gene sequence similarity of 98.99%. The genomic DNA G+C content of the novel strain was found to be 62.0 mol%. The predominant fatty acid composition was anteiso-$C_{15:0}$, anteiso-$C_{17:0}$ iso-$C_{16:0}$, and iso-$C_{15:0}$. Analysis of 16S rRNA gene sequences and DNA-DNA relatedness, as well as physiological and biochemical tests, showed genotypic and phenotypic differences between strain $SYB2^T$ and other Arthrobacter species. The type strain of the novel species was identified as $SYB2^T$ (=KCTC $19291^T$=DSM $19449^T$).