Histone methylation homeostasis is achieved by controlling the balance between methylation and demethylation to maintain chromatin function and developmental regulation. In animals, a conserved Jumonji C (JmjC) domain was found in a large group of histone demethylases. However, it is still unclear whether plants also contain the JmjC domain-containing active histone demethylases. Here we performed genome-wide screen and phylogenetic analysis of JmjC domain-containing proteins in the dicot plant, Arabidopsis, and monocot plant rice, and found 21 and 20 JmjC domain-containing, respectively. We also examined the expression of JmjC domain-containing proteins and compared them to human JmjC counterparts for potential enzymatic activity. The spatial expression patterns of the Arabidopsis JmjC domain-containing genes revealed that they are all actively transcribed genes. These active plant JmjC domain-containing genes could possibly function in epigenetic regulation to antagonize the activity of the large number of putative SET domain-containing histone methyltransferase activity to dynamically regulate histone methylation homeostasis.