Surface functionalities of activated carbon can be affected by the presence of heteroatoms such as oxygen, sulfur, and nitrogen. In this work, nitrogen-doped activated carbons (NACs) were prepared from shrimp shells, and the effects of the mixing ratio (raw material to an activating agent) on the porous texture and surface functionalities were investigated. It was found that, with increasing the mixing ratio (resulting in increasing N/C), the development of mesoporosity was significantly observed. This led to decreasing microporosity and specific surface areas (SSAs). The obtained NACs exhibited nitrogen functionalities in the forms of pyridinic and pyrrolic groups. It was found that although the pyridinic-N has a detrimental effect on the SSA, it does favor the pseudocapacitance, leading to an enhancement in the ion storage capability regardless of the low SSA.