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Frost is a climatic phenomenon in which water is at or below freezing point. A frost day refers to a day when the temperature goes down under zero Celsius degree throughout the night. Frost has important impacts on various aspects of human life, especially on agriculture and food productions. In the current study, the non-parametric (Mann-Kendall), parametric (Pearson correlation coefficient) and Innovative Trend Analysis (Sen) procedures were used to evaluate the effects of changing the trend of frost threshold in Northwest area of Iran. Based on Mann-Kendall and Pearson tests, there was a negative trend at Ardebil, Parsabad, Makoo, Maragheh and Mahabad stations, however, this effect was significant only at Ardebil station (p<0.05, Mann-Kendall). When Innovative Trend Analysis (Sen) method was used for Mahabad station, a decreasing trend was found for all values, while this method had no trend in Maragheh station. Tabriz and Makoo stations showed negative trends only in a small band (5%) while other values at two bands had no trend. Except for small band (10%), Ardebil station showed a negative trend in other values. Urmia, Parsabad, and Khoy stations had a negative and positive trend in some cases, respectively. Evaluation of threshold changes of the climatic phenomenon can lead to making better decisions especially about agriculture, water resources management and climate change adaptation strategies in this region of the country.