Civil structures are quite vulnerable to extreme dynamic loads as well as to natural disasters. The aforementioned problem is well-known, and, interestingly, unavoidable as it almost impossible to know when that type of loads or disasters are going to hit the existing structures. Due to such unpredictability, many are interested to adopt the online or real-time control and monitoring strategy instead of conventional approach. However, still off-line monitoring and vibration control strategies are useful to understand the overall performance of the investigated dynamical problem as it might not be an option to go for online due to feasibility or other constrains. It order to hold a debate, herein, the controlled performance of a multi-degree-of-freedom system has investigated both adopting off-line and online approaches. The linear-quadratic regulator (LQR) algorithm has been employed as control law and it is assumed that controller will behave as active control system. In order to understand the effect of the optimal control, the displacements and velocities at different degree-of-freedom's level have considered and compared. The outcome suggest that both approaches have advantages and disadvantages such as offline approach is quite useful to understand at the design phase of the project while online approach might be very effected after the construction.