We report on recent IR observations of the Be/X-ray binary system SAX J2103.5+4545/ CGS 03588-00834, obtained with the 1.52 m Carlos Sánchez Telescope (Observatorio de Izaña, Tenerife, Spain), and on the evolution of the H-alpha equivalent width for this system measured with the spectrograph Albireo, at the 1.5 m telescope of the Observatorio de Sierra Nevada (Granada, Spain). Observations from 2011 December 26 up to 2012 June 10 showed and IR enhancement of the optical counterpart CGS 03588-00834, with the brightness varying from J = 11.90 +/- 0.05 mag, H = 11.51 +/- 0.06 mag and Ks = 11.33 +/- 0.08 mag (MJD 55921.0), to J = 11.02 +/- 0.06 mag, H = 10.61 +/- 0.03 mag and Ks = 10.3 +/- 0.1 mag (MJD 56088.0).