Robotic minimally invasive surgery provides images from the intraoperative field including organs and sensitive anatomic structures whose protection from non-voluntary destruction is imperative. To assist the surgeon, control methods that discourage motions towards these sensitive areas are advocated in the related literature. In this work, an active constraint controller is proposed and is proved to guarantee that sensitive/forbidden areas defined by a point cloud are never violated by the tool tip while the closed loop system remains passive and its state bounded under the exertion of a human guiding force. Experimental results are given utilizing a KUKA LWR4+ kinesthetically guided in a virtual surgical environment. I. INTRODUCTION Robotic Minimally Invasive Surgery (RMIS) is a type of Minimally Invasive Surgery (MIS) which utilizes a masterslave manipulator system [1], [2]. MIS procedures are performed with elongated instruments through tiny incisions in the skin of the patient [3] thus minimum incurring intraoperative damage to the patients body. The advantages are many including the decreased cost of post-operative complications [4]. However, as surgeons in MIS manually operate the tools with their hands they may undergo fatigue in lengthy operations which deteriorate their performance. In an effort to overcome the problems of MIS while retaining its advantages, RMIS has been used [1]. RMIS is able to provide 3D vision, motion scaling, visual immersion and tremor filtration. Images from the intraoperative space are provided by an endoscopic camera as point-clouds in their raw-form. These images include organs and sensitive areas such as vessels and delicate tissues. To avoid involuntary destruction of these sensitive anatomic structures owing to the surgeon's strain, the implementation of control methods that discourage motions towards these sensitive areas has been proposed [5], [6]. Control methods that enforce Active Constraints (AC) or Virtual Fixtures (VF) are promising solutions among them.