The microstructure and positive temperature coefficient of resistivity (PTCR) characteristics of 0.1 mol%$Na_2Ti_6O_{13}$ doped $0.94BaTiO_3-0.06(Bi_{0.5}Na_{0.5})TiO_3$ (BBNT-NT001) ceramics sintered at various temperatures from $1200^{circ}C$ to $1350^{circ}C$ were investigated in order to develop eco-friendly PTCR thermistors with a high Curie temperature ($T_C$). Resulting thermistors showed a perovskite structure with a tetragonal symmetry. When sintered at $1200^{circ}C$, the specimen had a uniform microstructure with small grains. However, abnormally grown grains started to appear at $1250^{circ}C$ and a homogeneous microstructure with large grains was exhibited when the sintering temperature reached $1325^{circ}C$. When the temperature exceeded $1325^{circ}C$, the grain growth was inhibited due to the numerous nucleation sites generated at the extremely high temperature. It is considered that $Na_2Ti_6O_{13}$ is responsible for the grain growth of the $0.94BaTiO_3-0.06(Bi_{0.5}Na_{0.5})TiO_3$) ceramics by forming a liquid phase during the sintering at around $1300^{circ}C$. The grain growth of the BBNT-NT001 ceramics was significantly correlated with a decrease of resistivity. All the specimens were observed to have PTCR characteristics except for the sample sintered at $1200^{circ}C$. The BBNT-NT001 ceramics had significantly decreased $ ilde{n}_{rt}$ and increased resistivity jump with increasing sintering temperature at from $1200^{circ}C$ to $1325^{circ}C$. Especially, the BBNT-NT001 ceramics sintered at $1325^{circ}C$ exhibited superior PTCR characteristics of low resistivity at room temperature ($122;{Omega}{cdot}cm$), high resistivity jump ($1.28{ imes}10^4$), high resistivity temperature factor (20.4%/$^{circ}C$), and a high Tc of $157.9^{circ}C$.