Quasi-periodic oscillations (QPOs) are an important observable in accretion disk systems, and have been extensively studied in galactic x-ray binaries (XRB). QPOs should be present in Active Galactic Nuclei (AGN), as it is believed that galactic black holes and supermassive black holes (SMBH) are governed by a common set of physical processes. Possible explanations for QPOs include various combinations of the Keplerian motion of matter in the disk, rotation of the central compact object, general relativistic effects, or beat frequencies between two of the previous mechanisms. However, the search for QPOs in AGN has proven difficult, as the timescales would be much longer, due to their higher mass. Some candidate QPOs remain unconfirmed, but two reasonably strong cases have been found in XMM-Newton data with periods in the range ∼1-2 hours. Based on a mass estimate for REJ 1034+396, its QPO has been scaled to match a 67-Hz QPO in the BHXRB GRS1915+105. AGN monitoring was performed for many sources with the Rossi X-ray Timing Explorer (RXTE) satellite between 1996 and 2011. Reduced 3-color light curves were prepared and archived at University of California, San Diego (UCSD). We have investigated more than 50 sources for possible QPOs using the Lomb-Scargle periodogram (LSP), which is appropriate for unevenly sampled data. A QPO with period ~6 weeks has been reported in NGC 4945 (Smith et al ApJ submitted). A total of 1432 RXTE observations were made of the Seyfert-1 AGN, MKN 110. During a large cluster of observations in 2005-2012 (1,393 observations), the LSP shows a candidate QPO at 0.011 μHz (period = 1083.5 days).