Pseudorandom number generators are required to generate pseudorandom numbers which have not only good statistical properties but also unpredictability in cryptography. A geometric sequence is a sequence given by applying a nonlinear feedforward function to an m-sequence. Nogami, Tada and Uehara proposed a geometric sequence whose nonlinear feedforward function is given by the Legendre symbol, and showed the period, periodic autocorrelation and linear complexity of the sequence. Furthermore, Nogami et al. proposed a generalization of the sequence (this sequence is referred to as the generalized NTU sequence), and showed the period and periodic autocorrelation. In this paper, we investigate the linear complexity of the generalized NTU sequences. Under some conditions, we can ensure that generalized NTU sequences have large linear complexity from the results on linear complexity of Sidel'nikov sequences.