A mixed fraction contains a whole number part and a fractional part. The fraction should necessarily be a proper fraction.
A mixed fraction is the sum of a whole number and a proper fraction. Hence the statement is true. We generally use mixed fractions to quantify things which lie between two consecutive whole numbers. For example, the weight of a person lying between 50 and 51 kilograms is a mixed fraction, the length of a pole lying between 2m and 3m is a mixed fraction, etc.