Prior research has found the ratio of fronto‐central theta (4–7 Hz) and beta oscillations (13–30 Hz), known as the theta-beta ratio, to be negatively correlated with attentional control, reinforcement learning, executive function, and age. While theta-beta ratios have been found to decrease with age in adolescents and undergraduate samples, theta has been found to increase with age in older adults. Moreover, age‐related decreases in individual peak alpha frequency may be artifactually inflating theta with age. Collectively, these factors lead to an incomplete understanding of how theta-beta ratio varies across the lifespan, particularly in older adults. We conducted a preregistered analysis of data from the Midlife in the US (MIDUS) study examining the cross‐sectional associations between resting theta-beta ratio, age, and individual peak alpha frequency (n = 264; age 36–84, M = 55.7, SD = 11.0). Age was negatively correlated with theta-beta ratios and individual peak alpha frequencies. Although we also observed a significant negative correlation between theta and individual peak alpha frequencies, the relationship between theta and age was only apparent in exploratory analyses controlling for individual peak alpha frequency and beta. Notably, the correlation between theta-beta ratios and age remained after controlling for individual peak alpha frequencies. Our results replicate previous observations that theta-beta ratios and individual peak alpha frequencies are cross‐sectionally associated with age, and show that age‐related decreases in theta-beta ratios are not due to age‐related decreases in individual peak alpha frequencies.