The goal of this study is to explore the efficacy and safety of transcranial alternating current stimulation (tACS) in patients with mild Alzheimer's disease (AD). The study will recruit 40 individuals with mild AD with evidence of amyloid plaques in the brain through Positron Emission Tomography (PET) imaging. Participants will undergo baseline cognitive assessment, structural and functional MRI characterization, PiB-PET, and resting-state EEG measurement. The participants will be randomized to either a tACS group or a sham stimulation group. At the end of the intervention and 3-month follow-up, all subjects will repeat the baseline assessments.