MATRICS Consensus Cognitive Battery (MCCB) is a contemporary standard for assessment of cognitive functions in schizophrenia. The aim of the study was to examine the association between electroencephalographic spectral power and a wide range of cognitive functions measured with MCCB. Thirty-nine patients with schizophrenia (27 male, mean age 28.2 ± 5.2 years) underwent EEG recordings and were assessed with MCCB. The EEG recordings were visually inspected and manually cleaned from artifacts and subjected to spectral analysis with EEGlab. Absolute and relative power as percentage of total spectral power were computed for frequency ranges from 0.5 to 30 Hz. To compare spectral power in patients with various cognitive functioning, patients from best and worst MCCB quartiles were selected. Superior cognitive performance was associated with less power of theta waves. Six MCCB cognitive tests showed significant correlations with absolute theta power and three tests with relative theta power. The correlation coefficients between MCCB composite score and theta power were r_p = −0.45 for absolute and r_p = −0.36 for relative values. Increased theta power was linked especially to memory deficits. These preliminary results suggest that electroencephalographic resting state theta power is an indicator of cognitive deficit in patients with schizophrenia.