No, they are not. The final N in “brown” must be pronounced (while allowing air to flow out of the nose, the airflow is stopped in the mouth using the tongue in the same position as for a T or D). In real life, the preceding vowel is usually nasalized by most speakers in anticipation of the final N, but this pre-nasalization is a secondary feature.
Some speakers may also nasalize the vowel in “brow”, but that is not considered standard, and in any event, they would not stop the airflow in the mouth at the end of the word (unlike “brown”). Such nasalization (without the final stopping of the oral air flow) should be ignored.