Allergic rhinitis (AR) is the most common chronic allergic disease in school-age children. An increased prevalence of attention deficit hyperactivity disorder (ADHD) in AR patients has been reported; however, inattention and hyperactivity in AR children have not been investigated using objective and scientific measurements. Methods: We used AR symptom score, ADHD symptom scale, and computerized continuous performance test (CPT) to study the attention and impulsivity in AR children, age-matched controls, and ADHD children (aged 6–15 years). Univariate and multivariate linear regression analyses were applied to identify risk factors for impulsivity and inattention in AR children. Results: Twenty-nine controls, 10 ADHD, and 105 AR children were enrolled. There were no differences in age and sex among the three groups. The scores of Hyperactivity/Impulsivity subscales of ADHD symptoms from both parents and teachers were significantly higher in the AR children. The CPT in AR children revealed higher commission errors, shorter reaction times, and more perseveration. Risk factors for inattention and impulsivity in AR children included younger age, male sex, higher AR symptom scores, persistent AR, moderate/severe AR, multiple atopic diseases, family history of atopy, and possible comorbidity with ADHD. Conclusion: Care for AR children should not only involve treating their allergy, but also monitoring the possible comorbidities of impulsivity and inattention. In children with impulsivity, AR should be considered in addition to ADHD.