Many wireless devices in common use today are worn either on or in close proximity to the body. Those devices are designed for applications such as activity or vital-signs monitoring, typically using Bluetooth/Zigbee technology to communicate with external devices under body-centric wireless communications system (BWCS). In addition, currently, microwave tomography (MWT) system is widely researched since it offers a portable, affordable and non-invasively modality. Study on interaction between the human body and electromagnetic (EM) waves inevitably must be evaluated for wearable and implantable antennas for BWCS or antennas/array for MWT system. Basically, the EM interaction includes two ways: an influence of the human body on the performance of antennas and an influence of EM waves on the human body. This paper studies on such phenomenon by designing two numerical phantom models particularly for head phantom, i.e. a homogeneous phantom model and multilayer phantom at 5.8 GHz. As for the head homogeneous phantom, it is set as a skull-mimicking tissue, whose permittivity and conductivity are set equally at 5.8 GHz. The multilayer head phantom is constructed by six layers namely skin, fat, skull, CSF (cerebrospinal fluid), brain and muscle. In this paper, a dipole is then put in proximity to the head phantom models for investigating the influence of such models on its performances at 5.8 GHz due to EM field interaction. The results show that the frequency center of dipole antenna tends to shift at lower frequency when situated close to the head phantom, comparing to the simulation in free space. Moreover, the width of beam-pattern of the dipole is significantly affected by phantom's structure. Finally, it can be stated that different structure of tissue-mimicking model will affect different phenomenon due to absorption properties for each structure.