We present wide-field $JHK_s$-band photometric observations of the three compact H II regions G48.9-0.3, G49.0-0.3, and G49.2-0.3 in the active star-forming region W51B. The star clusters inside the three compact H II regions show the excess number of stars in the $J-K_s$ histograms compared with reference fields. While the mean color excess ratio $(E_{J-H}/E_{H-K_s})$ of the three compact H II regions are similar to ${sim}2.07$, the visual extinctions toward them are somewhat different: ${sim}17$ mag for G48.9-0.3 and G49.0-0.3; ${sim}23$ mag for G49.2-0.3. Based on their sizes and brightnesses, we suggest that the age of each compact H II region is ${leq}2;Myr$. The inferred total stellar mass, ${sim}1.4{ imes}10^4M_{odot}$, of W51B makes it one of the most active star forming regions in the Galaxy with the star formation efficiency of ${sim}10%$.