In recent times, the popularity of seeds, other than cereals, in the diet has systematically grown. The fat contained in these products significantly affects their energy value as well as their biological and physicochemical properties, including their susceptibility to oxidation. The objective of this study is to evaluate the fat concentration and fatty acid (FA) composition of popular non-spice seeds used in food as a substitute for cereals or a functional additive. The research material consisted of thirteen groups of seeds derived from the following plants: amaranth, blue poppy, buckwheat, chia, flax, hemp, canihua, milk thistle, pumpkin, plantago, quinoa, sesame, and sunflower. The fat contents and fatty acid profiles differed significantly between the tested products and were dependent on the plant species. In all products, polyunsaturated fatty acids (PUFAs, 40–80% of total FAs) dominated. Linoleic acid was the main FAs in most tested seeds. The exceptions were chia and flax seeds, which were characterized by very high contents of α-linolenic acid, respectively, 62.0 and 51.4% of the total FAs. The share of monounsaturated FAs (mainly oleic acid) in the total FAs content was between 6 and 40%. All tested seeds (especially flax, chia, and hemp) have favorable values for their indexes of atherogenicity and thrombogenicity as well as the hypocholesterolemic/hypercholesterolemic ratio.