Abstract— Actual values of the mechanical parameters of isolation system elements of semi-active isolated buildings may deviate from their design values. Therefore, it is more realistic to evaluate their seismic performance via use of probabilistic analyses methods. While the mean values of random variables are used as nominal design values in a probabilistic model, their coefficients of variation (c.o.v.) represent the level of uncertainty. In the absence of adequate statistical observation for determining suitable c.o.v values of random semi-active isolation system parameters, it is worth evaluating the sensitivity of the seismic response to the aforementioned c.o.v values. Here, this issue is examined in the context of a low-rise benchmark semi-active isolated building under historical near-fault earthquakes. Cumulative distribution plots of peak base displacements and top floor accelerations are presented for different c.o.v values which shows that as the covariance values increase, the range of results expand depending on the earthquake data.