deselect.py

bl_info = {
    "name": "Deselect Active Button",
    "author": "Anonymous",
    "version": (1, 0),
    "blender": (2, 79, 5),
    "location": "View3D > Tool Shelf > Misc",
    "description": "Deselect Active",
    "warning": "",
    "wiki_url": "",
    "category": "User",
}

import bpy

def main(context):
   bpy.context.scene.objects.active.select = False

class DeselectActiveOperator(bpy.types.Operator):
    bl_idname = "object.deselect_active_operator"
    bl_label = "Deselect Active"

    def execute(self,context):
        main(context)
        return {'FINISHED'}

class DeselectActivePanel(bpy.types.Panel):
    bl_label = "Deselect Active"
    bl_idname = "DeselectActivePanel_Operator"
    bl_space_type = 'VIEW_3D'
    bl_region_type = 'TOOLS'
    bl_category = "Misc"

    def draw(self, context):
        layout = self.layout

        row = layout.row()
        row.operator("object.deselect_active_operator")

def register():
    bpy.utils.register_class(DeselectActiveOperator)
    bpy.utils.register_class(DeselectActivePanel)

def unregister():
    bpy.utils.unregister_class(DeselectActiveOperator)
    bpy.utils.unregister_class(DeselectActivePanel)


if __name__ == "__main__":
    register()