An apparatus for non-invasively estimating bio-information and a method of determining whether a bio-signal is normal by the apparatus for estimating bio-information are provided. The apparatus for estimating bio-information according to an embodiment of the disclosure includes: a photoplethysmogram (PPG) sensor configured to measure a PPG signal from an object; and a processor configured to extract a plurality of pairs of local maximum points and local minimum points from a second derivative signal of the PPG signal, to select at least one reference pair from among the extracted plurality of pairs, and to determine whether the PPG signal is normal based on the selected at least one reference pair.