The aim of this study is to evaluate the probability of seismic hazard for the Taipei metropolitan area in northern Taiwan from readily available information, including the attenuation relationship of peak ground acceleration (PGA), tectonic settings, fault-slip data, and seismicity. The PGA seismic hazard mapping reveals that the hazard level in this area increases going from northwest to southeast and southwest. There are four important earthquake sources that contribute to the hazard level: (1) the plate-boundary interface (subduction zone interface) located offshore of the Ilan plain; (2) the intraslab subduction zone underneath Taipei itself; (3) the crustal areal sources in eastern Taiwan and central Taiwan; and (4) the nearby active Shanchiao fault. The slip-rate of the targeted fault is relatively low, and therefore not the most dangerous earthquake source revealed in the 475-year return period. However, there is no doubt that the target fault is the control source in the 2475-year return period. Furthermore, higher PGAs are predicted using the attenuation relationship of subduction zone earthquake sources rather than crustal earthquake sources, meaning an increase of the seismic hazard level over previous estimates. Consequently, more attention needs to be paid to subduction zone sources when considering mitigation of seismic hazards in northern Taiwan.