<p>With the rapid advancement of 5G and Wi-Fi 6E systems, there is a growing demand for flexible, low-power, and tunable radio frequency (RF) components. Traditional tunable filters, often based on rigid substrates or high-voltage tuning mechanisms, lack the flexibility and energy efficiency required for next-generation wearable and portable communication devices. To address this gap, this paper presents the design, fabrication, and characterization of a three-state flexible tunable bandpass filter based on organic electrochemical transistors (OECTs). The filter is fabricated on a PET substrate using a screen-printing process, with OECTs integrated into the resonator structure to enable low-voltage electrical tuning. Experimental results demonstrate that the filter achieves three distinct tuning states within the frequency range of 4.37–5.45 GHz, covering both 5G NR n79 and Wi-Fi 6E bands. Key performance metrics include an insertion loss of 1.65–1.87 dB, return loss close to 20 dB, and an ON/OFF ratio exceeding 10³, all achieved with only a 1.3 V bias voltage. The filter also maintains stable performance under mechanical bending, confirming its suitability for flexible electronics. This work highlights the potential of OECT-based tuning for next-generation flexible RF systems, offering a compelling combination of low-voltage operation, low loss, high tunability, and scalable fabrication.</p>