As a complex phenomenon, musical improvisation can be addressed from the perspective of different disciplines. In music therapy, improvisation is a central practice; however, as a technique, it lacks methodological guidelines and scientific evidence justifying its use. The aim of this study was to investigate the social interaction features that emerge during group musical improvisation. We conducted a mixed methods study with an exploratory sequential design comparing improvisation and imitation tasks, performed by groups of younger and older adults, separately, by generating and analyzing six categories of nonverbal communication and social interaction.Younger (n = 131) and older adults (n = 110) participated in one of two types of music activities: group musical improvisation or group rhythmic imitation. Eight group musical improvisation tasks ? as implemented in music therapy settings ? were compared with eight group rhythmic imitation tasks, according to six categories of analysis: visual contact, body movement, type of production, music interaction, vocal aspect, and leadership.Statistical analysis using a Chi-square test (χ2) showed greater social interaction among the participants of the improvisation groups than among those in the rhythmic imitation groups, in both age ranges.Our results provide specific evidence for this type of music task and a complementary approach to musical improvisation analysis, contributing to the knowledge of music therapy.