Objective: This exploratory study aimed to evaluate the effects of electroacupuncture (EA) on pain and functional outcomes in patients with chronic nonspecific low back pain (CNLBP), and to investigate objective peripheral physiological responses associated with clinical improvement. Methods: In this prospective, double-blind, randomized sham-controlled trial, adults with CNLBP received EA at Shenshu (BL23) and an ipsilateral Ashi acupoint three times weekly for 2 weeks, followed by a 4-week follow-up. The primary outcome was pain intensity assessed by the Numeric Rating Scale (NRS), with responder analysis based on the minimal clinically important difference (MCID; ΔNRS ≥ 2). Secondary outcomes included the Oswestry Disability Index (ODI), local microcirculatory perfusion, skin temperature, and muscle tissue properties. Results: Compared with sham EA, EA significantly reduced pain intensity after the first session, after six sessions, and at follow-up (p < 0.003; r = 0.70–0.84). MCID responder rates were significantly higher in the EA group after the first session, six sessions and at follow-up (p < 0.003; RR = 3.75 and 6.00 after six sessions and follow-up, respectively). EA increased local blood flow at BL23 after the first and sixth sessions. Skin temperature showed only a transient within-group increase, without a significant adjusted between-group difference. Similar trends were observed at Ashi acupoint, and increased blood flow was associated with pain improvement. Conclusions: EA improved pain and functional outcomes in patients with CNLBP while inducing measurable peripheral vascular and physiological responses. Increased local blood flow may represent a candidate physiological correlate of EA-related symptom improvement. These findings support the exploration of objective physiological markers in acupuncture research.