Introduction: Terbium-149 (¹⁴⁹Tb) is a promising radionuclide for targeted α therapy that has a non-zero branching ratio (BR) for positron decay. However, its relatively low positron branching fraction and multiple prompt γ emissions may challenge quantitative imaging. This study evaluates, for the first time, the imaging performance and quantitative accuracy of ¹⁴⁹Tb using a clinical long axial field-of-view (LAFOV) PET/CT system. Methods: Quantitative accuracy of ¹⁴⁹Tb was assessed with a NEMA IEC body phantom, which was filled with about 45 MBq ¹⁴⁹Tb and a sphere-to-background ration of 10:1. The phantom was scanned for 20 min and shorter scan times and lower activities were simulated. Recovery coefficients, coefficient of variation, and lung residual error were evaluated for different reconstruction settings and compared to the EARL standard 2 for ¹⁸F. Results: High-quality PET images of ¹⁴⁹Tb were obtained, even with a simulated total activity of 4.5 MBq. The 20 min and full activity scan yielded a mean recovery coefficient RCₜₑₓₜᵢₜmean of 0.55, 0.69, 0.73, 0.76, 0.79, and 0.81 for the six phantom spheres. Despite the low count statistics, the coefficient of variation stays mostly below 15 %. Relative scatter correction combined with prompt γ modeling provided robust quantification. Conclusion: ¹⁴⁹Tb can be imaged using a commercial LAFOV PET/CT with a quantitative accuracy comparable to the EARL standard 2 for ¹⁸F. These findings demonstrate the feasibility of PET-based treatment verification and dosimetry for targeted α therapy with ¹⁴⁹Tb.