This paper presents the identification of the modal properties of a full-scale 5-story reinforced concrete (R/C) building outfitted with a variety of nonstructural components and systems (NCSs) tested on the unidirectional NEES-UCSD shake table in April-May, 2012. The building specimen was tested under base-isolated (BI) and fixed-base (FB) configurations. The purpose of the test program was to study the seismic response of the structure and NCSs and their dynamic interaction at different levels of seismic excitation. For each base configuration (BI and FB), the building was subjected to a sequence of earthquake base motions carefully selected so as to progressively increase the seismic demand on the structure and NCSs. Before and after each seismic test, ambient vibration (AV) data were recorded, and additionally, low amplitude white noise (WN) base excitation tests were conducted at key stages during the test protocol. Because of the low intensity of the ambient and WN base excitations, a quasi-linear response of the system is assumed, and the modal parameters of an equivalent linear time-invariant (LTI) model are estimated. Using the structural vibration data recorded by 28 accelerometers, three system identification methods, including two output-only (SSI-DATA and NExT-ERA) and one input-output (DSI), are used to estimate the modal properties of the BI and FB building between seismic tests. The results show that the modal properties obtained by different methods are in good agreement and that the estimated modal parameters of the building are affected by the amplitude of the excitation, environmental conditions, and structural/nonstructural damage in the structure.