Background: The case of sexual behavior in adolescents is increasingly worrisome because teenage sexual behavior is now exceeding the limits and quite alarming. This is supported by research an increasing pattern in adolescent pregnancy in sub-Sahara Africa. Methods: An interviewer-administered structured questionnaire was used to conduct a cross-sectional study of knowledge and perception of 200 adolescent females was carried out in a semi-urban area in Rivers state, Nigeria. Results: About 61% of the respondents are reportedly sexually active and 39% are not sexually active while 70.0% of the respondents had poor knowledge of teenage pregnancy and 30.0% had good knowledge of teenage pregnancy. About 33.3% of respondents with good knowledge of teenage pregnancy was between 13 – 16 years old and 56.67% of individuals with good knowledge had tertiary education. It was observed that 76% of the sexually active respondents had poor knowledge of teenage pregnancy and only 60.3% of the non-sexually active persons had poor knowledge. The analysis shows that most of the sexually active persons had poor knowledge of teenage pregnancy (chi-square = 5.78 p =0.016) and the likelihood of poor knowledge was 1.2 times (95% C.I: 1.0 – 1.5) more among the sexually active adolescents. The findings also showed that 52% think peer pressure leads to teenage pregnancy, 78% indicated that poor sexual education at school lead to teenage pregnancy, 71.5% indicated that substance abuse led to teenage pregnancy. Other factors and consequences as indicated by the respondents include: Unsupervised teenagers (83.5%), rape (86.5%), social media (81.5%), Poverty (72.0%), Unsafe abortion (87.5%), stigma and isolation (93.5%). Conclusion: The study showed a relatively poor knowledge of teenage pregnancy especially among sexually active female adolescents. Sexual education and increased awareness are recommended to curb the spread of teen pregnancy in this region.