This is the database for the study entitled Shear-wave elastography for assessment of trapezius muscle stiffness: reliability and association with low-level muscle activity. In this study, we explored the reliability of shear-wave elastography for assessment of the trapezius muscle stiffness and its relationship with low-level muscle activity.Twenty participants were included in a two-session experiment. Measurements of shear modulus and muscle activity were performed at rest and during low-level activity, induced by shoulder abduction without additional external resistance. Good to excellent intra-session repeatability (ICC > 0.80) and moderate inter-rater and inter-session reproducibility (ICC = 0.66-0.74) were observed. Typical errors were acceptable only for intra-session measurements in resting conditions. Inverse relationships between shear modulus and muscle activity at 40° and 60° of shoulder abduction (r = -0.53 and -0.57) were observed on a group level. We also found lower shear modulus in females, for perpendicular probe position and for the non-dominant side of the body. Previous studies have demonstrated positive within-individual relationships between muscle activity and shear modulus. Our results suggested that, at least when the activity levels are low, an inverse relationship exists between muscle activity and shear modulus on a group level, suggesting inherent passive stiffness could account for a larger portion of the variance (compared to muscle activity) in shear modulus when the muscle activity is low. Our results imply that shear-wave elastography can be used in research exploring muscle stiffness, however, caution is needed since only intra-session examination in resting conditions showed acceptable within-participant typical errors.